Golang for Node.js Developers

Examples of Golang examples compared to Node.js for learning

This guide full of examples is intended for people learning Go that are coming from Node.js, although the vice versa can work too. This is not meant to be a complete guide and it is assumed that you've gone through the Tour of Go tutorial. This guide is meant to be barely good enough to help you at a high level understand how to do X in Y and doing further learning on your own is of course required.

Contents

• Examples
  • comments
  • printing
  • logging
  • variables
  • types
    • bool
    • number
    • string
    • array
    • object
    • function
  • type check
  • interpolation
  • if/else
    • ternary
  • for
  • while
  • switch
  • arrays
    • slicing
    • copying
    • appending
    • prepending
  • uint8 arrays
  • array iteration
    • looping
    • mapping
    • filtering
    • reducing
    • sorting
  • buffers
    • allocate
    • big endian
    • little endian
    • hex
    • compare
    • equals
  • maps
    • iteration
  • objects
  • functions
  • default values
  • destructuring
  • spread operator
  • rest operator
  • swapping
  • classes
    • constructors
    • instantiation
    • "this"
  • generators
  • datetime
    • parsing
    • formatting
    • unix timestamp
  • timeout
  • interval
  • IIFE
  • files
    • creating
    • opening
    • writing
    • reading
    • closing
    • deleting
    • file descriptors
  • json
    • parse
    • stringify
  • big numbers
    • uint
    • string
    • hex
    • buffers
    • compare
    • equals
  • promises
    • then
    • all
  • async/await
  • streams
    • reading
    • writing
  • event emitter
  • errors
  • try/catch
  • exceptions
  • regex
  • exec (sync)
  • exec (async)
  • tcp server
  • udp server
  • http server
  • url parse
  • gzip
    • compress
    • decompress
  • dns
    • ns lookup
    • ip lookup
    • mx lookup
    • txt lookup
    • set resolution servers
  • crypto
    • sha256
  • env vars
  • cli args
  • cli flags
  • stdout
  • stderr
  • stdin
  • modules
    • installing
    • updating
    • removing
    • importing
    • exporting
    • publishing
  • stack trace
  • databases
    • sqlite3
  • testing
  • benchmarking
  • documentation
• Contributing
• License

Examples

All sample code is available in examples/

comments

---

Node.js

// this is a line comment

/*
 this is a block comment
*/

Go

package main

func main() {
	// this is a line comment

	/*
	   this is a block comment
	*/
}

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printing

---

Node.js

console.log('print to stdout')
console.log('format %s %d', 'example', 1)
console.error('print to stderr')

Output

print to stdout
format example 1
print to stderr

Go

package main

import (
	"fmt"
	"os"
)

func main() {
	fmt.Println("print to stdout")
	fmt.Printf("format %s %v\n", "example", 1)
	fmt.Fprintf(os.Stderr, "print to stderr")
}

Output

print to stdout
format example 1
print to stderr

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logging

---

Node.js

console.log((new Date()).toISOString(), 'hello world')

Output

2021-04-11T20:55:07.451Z hello world

Go

package main

import "log"

func main() {
	log.Println("hello world")
}

Output

2021/04/11 13:55:07 hello world

(Package log writes to standard error ánd prints the date and time of each logged message)

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variables

---

Node.js

// function scoped
var foo = 'foo'

// block scoped
let bar = 'bar'

// constant
const qux = 'qux'

Go

(variables are block scoped in Go)

package main

func main() {
	// explicit
	var foo string = "foo"

	// type inferred
	var bar = "foo"

	// shorthand
	baz := "bar"

	// constant
	const qux = "qux"
}

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interpolation

---

Node.js

const name = 'bob'
const age = 21
const message = `${name} is ${age} years old`

console.log(message)

Output

bob is 21 years old

Go

package main

import "fmt"

func main() {
	name := "bob"
	age := 21
	message := fmt.Sprintf("%s is %d years old", name, age)

	fmt.Println(message)
}

Output

bob is 21 years old

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types

---

Node.js

// primitives
const myBool = true
const myNumber = 10
const myString = 'foo'
const mySymbol = Symbol('bar')
const myNull = null
const myUndefined = undefined

// object types
const myObject = {}
const myArray = []
const myFunction = function() {}
const myError = new Error('error')
const myDate = new Date()
const myRegex = /a/
const myMap = new Map()
const mySet = new Set()
const myPromise = Promise.resolve()
const myGenerator = function *() {}
const myClass = class {}

Go

package main

func main() {
	// primitives
	var myBool bool = true
	var myInt int = 10
	var myInt8 int8 = 10
	var myInt16 int16 = 10
	var myInt32 int32 = 10
	var myInt64 int64 = 10
	var myUint uint = 10
	var myUint8 uint8 = 10
	var myUint16 uint16 = 10
	var myUint32 uint32 = 10
	var myUint64 uint64 = 10
	var myUintptr uintptr = 10
	var myFloat32 float32 = 10.5
	var myFloat64 float64 = 10.5
	var myComplex64 complex64 = -1 + 10i
	var myComplex128 complex128 = -1 + 10i
	var myString string = "foo"
	var myByte byte = 10  // alias to uint8
	var myRune rune = 'a' // alias to int32

	// composite types
	var myStruct struct{} = struct{}{}
	var myArray []string = []string{}
	var myMap map[string]int = map[string]int{}
	var myFunction func() = func() {}
	var myChannel chan bool = make(chan bool)
	var myInterface interface{} = nil
	var myPointer *int = new(int)
}

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type check

---

Node.js

function typeOf(obj) {
  return {}.toString.call(obj).split(' ')[1].slice(0,-1).toLowerCase()
}

const values = [
  true,
  10,
  'foo',
  Symbol('bar'),
  null,
  undefined,
  NaN,
  {},
  [],
  function(){},
  new Error(),
  new Date(),
  /a/,
  new Map(),
  new Set(),
  Promise.resolve(),
  function *() {},
  class {},
]

for (value of values) {
  console.log(typeOf(value))
}

Output

boolean
number
string
symbol
null
undefined
number
object
array
function
error
date
regexp
map
set
promise
generatorfunction
function

Go

package main

import (
	"fmt"
	"reflect"
	"regexp"
	"time"
)

func main() {
	values := []interface{}{
		true,
		int8(10),
		int16(10),
		int32(10),
		int64(10),
		uint(10),
		uint8(10),
		uint16(10),
		uint32(10),
		uint64(10),
		uintptr(10),
		float32(10.5),
		float64(10.5),
		complex64(-1 + 10i),
		complex128(-1 + 10i),
		"foo",
		byte(10),
		'a',
		rune('a'),
		struct{}{},
		[]string{},
		map[string]int{},
		func() {},
		make(chan bool),
		nil,
		new(int),
		time.Now(),
		regexp.MustCompile(`^a$`),
	}

	for _, value := range values {
		fmt.Println(reflect.TypeOf(value))
	}
}

Output

bool
int8
int16
int32
int64
uint
uint8
uint16
uint32
uint64
uintptr
float32
float64
complex64
complex128
string
uint8
int32
int32
struct {}
[]string
map[string]int
func()
chan bool
<nil>
*int
time.Time
*regexp.Regexp

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if/else

---

Node.js

const array = [1, 2]

if (array) {
  console.log('array exists')
}

if (array.length === 2) {
  console.log('length is 2')
} else if (array.length === 1) {
  console.log('length is 1')
} else {
  console.log('length is other')
}

const isOddLength = array.length % 2 == 1 ? 'yes' : 'no'

console.log(isOddLength)

Output

array exists
length is 2
no

Go

package main

import "fmt"

func main() {
	array := []byte{1, 2}

	if array != nil {
		fmt.Println("array exists")
	}

	if len(array) == 2 {
		fmt.Println("length is 2")
	} else if len(array) == 1 {
		fmt.Println("length is 1")
	} else {
		fmt.Println("length is other")
	}

	// closest thing to ternary operator
	isOddLength := "no"
	if len(array)%2 == 1 {
		isOddLength = "yes"
	}

	fmt.Println(isOddLength)
}

Output

array exists
length is 2
no

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for

---

Node.js

for (let i = 0; i <= 5; i++) {
  console.log(i)
}

Output

0
1
2
3
4
5

Go

package main

import "fmt"

func main() {
	for i := 0; i <= 5; i++ {
		fmt.Println(i)
	}
}

Output

0
1
2
3
4
5

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while

---

Node.js

let i = 0

while (i <= 5) {
  console.log(i)

  i++
}

Output

0
1
2
3
4
5

Go

(there's no while keyword in Go but the same functionality is achieved by using for)

package main

import "fmt"

func main() {
	i := 0

	for i <= 5 {
		fmt.Println(i)

		i++
	}
}

Output

0
1
2
3
4
5

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switch

---

Node.js

const value = 'b'

switch(value) {
  case 'a':
    console.log('A')
    break
  case 'b':
    console.log('B')
    break
  case 'c':
    console.log('C')
    break
  default:
    console.log('first default')
}

switch(value) {
  case 'a':
    console.log('A - falling through')
  case 'b':
    console.log('B - falling through')
  case 'c':
    console.log('C - falling through')
  default:
    console.log('second default')
}

Output

B
B - falling through
C - falling through
second default

Go

package main

import "fmt"

func main() {
	value := "b"

	switch value {
	case "a":
		fmt.Println("A")
	case "b":
		fmt.Println("B")
	case "c":
		fmt.Println("C")
	default:
		fmt.Println("first default")
	}

	switch value {
	case "a":
		fmt.Println("A - falling through")
		fallthrough
	case "b":
		fmt.Println("B - falling through")
		fallthrough
	case "c":
		fmt.Println("C - falling through")
		fallthrough
	default:
		fmt.Println("second default")
	}
}

Output

B
B - falling through
C - falling through
second default

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arrays

---

Examples of slicing, copying, appending, and prepending arrays.

Node.js

const array = [1, 2, 3, 4, 5]
console.log(array)

const clone = array.slice(0)
console.log(clone)

const sub = array.slice(2,4)
console.log(sub)

const concatenated = clone.concat([6, 7])
console.log(concatenated)

const prepended = [-2,-1,0].concat(concatenated)
console.log(prepended)

Output

[ 1, 2, 3, 4, 5 ]
[ 1, 2, 3, 4, 5 ]
[ 3, 4 ]
[ 1, 2, 3, 4, 5, 6, 7 ]
[ -2, -1, 0, 1, 2, 3, 4, 5, 6, 7 ]

Go

package main

import "fmt"

func main() {
	array := []int{1, 2, 3, 4, 5}
	fmt.Println(array)

	clone := make([]int, len(array))
	copy(clone, array)
	fmt.Println(clone)

	sub := array[2:4]
	fmt.Println(sub)

	concatenated := append(array, []int{6, 7}...)
	fmt.Println(concatenated)

	prepended := append([]int{-2, -1, 0}, concatenated...)
	fmt.Println(prepended)
}

Output

[1 2 3 4 5]
[1 2 3 4 5]
[3 4]
[1 2 3 4 5 6 7]
[-2 -1 0 1 2 3 4 5 6 7]

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uint8 arrays

---

Node.js

const array = new Uint8Array(10)
console.log(array)

const offset = 1

array.set([1, 2, 3], offset)
console.log(array)

const sub = array.subarray(2)
console.log(sub)

const sub2 = array.subarray(2,4)
console.log(sub2)

console.log(array)
const value = 9
const start = 5
const end = 10
array.fill(value, start, end)
console.log(array)

console.log(array.byteLength)

Output

Uint8Array [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ]
Uint8Array [ 0, 1, 2, 3, 0, 0, 0, 0, 0, 0 ]
Uint8Array [ 2, 3, 0, 0, 0, 0, 0, 0 ]
Uint8Array [ 2, 3 ]
Uint8Array [ 0, 1, 2, 3, 0, 0, 0, 0, 0, 0 ]
Uint8Array [ 0, 1, 2, 3, 0, 9, 9, 9, 9, 9 ]
10

Go

package main

import "fmt"

func main() {
	array := make([]uint8, 10)
	fmt.Println(array)

	offset := 1

	copy(array[offset:], []uint8{1, 2, 3})
	fmt.Println(array)

	sub := array[2:]
	fmt.Println(sub)

	sub2 := array[2:4]
	fmt.Println(sub2)

	fmt.Println(array)
	value := uint8(9)
	start := 5
	end := 10
	for i := start; i < end; i++ {
		array[i] = value
	}
	fmt.Println(array)

	fmt.Println(len(array))
}

Output

[0 0 0 0 0 0 0 0 0 0]
[0 1 2 3 0 0 0 0 0 0]
[2 3 0 0 0 0 0 0]
[2 3]
[0 1 2 3 0 0 0 0 0 0]
[0 1 2 3 0 9 9 9 9 9]
10

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array iteration

---

Examples of iterating, mapping, filtering, and reducing arrays.

Node.js

const array = ['a', 'b', 'c']

array.forEach((value, i) => {
  console.log(i, value)
})

const mapped = array.map(value => {
  return value.toUpperCase()
})

console.log(mapped)

const filtered = array.filter((value, i) => {
  return i % 2 == 0
})

console.log(filtered)

const reduced = array.reduce((acc, value, i) => {
  if (i % 2 == 0) {
    acc.push(value.toUpperCase())
  }

  return acc
}, [])

console.log(reduced)

Output

0 'a'
1 'b'
2 'c'
[ 'A', 'B', 'C' ]
[ 'a', 'c' ]
[ 'A', 'C' ]

Go

package main

import (
	"fmt"
	"strings"
)

func main() {
	array := []string{"a", "b", "c"}

	for i, value := range array {
		fmt.Println(i, value)
	}

	mapped := make([]string, len(array))
	for i, value := range array {
		mapped[i] = strings.ToUpper(value)
	}

	fmt.Println(mapped)

	var filtered []string
	for i, value := range array {
		if i%2 == 0 {
			filtered = append(filtered, value)
		}
	}

	fmt.Println(filtered)

	var reduced []string
	for i, value := range array {
		if i%2 == 0 {
			reduced = append(reduced, strings.ToUpper(value))
		}
	}

	fmt.Println(reduced)
}

Output

0 a
1 b
2 c
[A B C]
[a c]
[A C]

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array sorting

---

Examples of how to sort an array

Node.js

const stringArray = ['a', 'd', 'z', 'b', 'c', 'y']
const stringArraySortedAsc = stringArray.sort((a, b) => a > b ? 1 : -1)
console.log(stringArraySortedAsc)

const stringArraySortedDesc = stringArray.sort((a, b) => a > b ? -1 : 1)
console.log(stringArraySortedDesc)


const numberArray = [1, 3, 5, 9, 4, 2, 0]
const numberArraySortedAsc = numberArray.sort((a, b) => a - b)
console.log(numberArraySortedAsc)

const numberArraySortedDesc = numberArray.sort((a, b) => b - a)
console.log(numberArraySortedDesc)

const collection = [
    {
        name: "Li L",
        age: 8
    },
    {
        name: "Json C",
        age: 3
    },
    {
        name: "Zack W",
        age: 15
    },
    {
        name: "Yi M",
        age: 2
    }
]

const collectionSortedByAgeAsc = collection.sort((a, b) => a.age - b.age)
console.log(collectionSortedByAgeAsc)

const collectionSortedByAgeDesc = collection.sort((a, b) => b.age - a.age)
console.log(collectionSortedByAgeDesc)

Output

[ 'a', 'b', 'c', 'd', 'y', 'z' ]
[ 'z', 'y', 'd', 'c', 'b', 'a' ]
[ 0, 1, 2, 3, 4, 5, 9 ]
[ 9, 5, 4, 3, 2, 1, 0 ]
[ { name: 'Yi M', age: 2 },
  { name: 'Json C', age: 3 },
  { name: 'Li L', age: 8 },
  { name: 'Zack W', age: 15 } ]
[ { name: 'Zack W', age: 15 },
  { name: 'Li L', age: 8 },
  { name: 'Json C', age: 3 },
  { name: 'Yi M', age: 2 } ]

Go

package main

import (
	"fmt"
	"sort"
)

type Person struct {
	Name string
	Age  int
}

type PersonCollection []Person

func (pc PersonCollection) Len() int {
	return len(pc)
}

func (pc PersonCollection) Swap(i, j int) {
	pc[i], pc[j] = pc[j], pc[i]
}

func (pc PersonCollection) Less(i, j int) bool {
	// asc
	return pc[i].Age < pc[j].Age
}

func main() {
	intList := []int{1, 3, 5, 9, 4, 2, 0}

	// asc
	sort.Ints(intList)
	fmt.Println(intList)
	// desc
	sort.Sort(sort.Reverse(sort.IntSlice(intList)))
	fmt.Println(intList)

	stringList := []string{"a", "d", "z", "b", "c", "y"}

	// asc
	sort.Strings(stringList)
	fmt.Println(stringList)
	// desc
	sort.Sort(sort.Reverse(sort.StringSlice(stringList)))
	fmt.Println(stringList)

	collection := []Person{
		{"Li L", 8},
		{"Json C", 3},
		{"Zack W", 15},
		{"Yi M", 2},
	}

	// asc
	sort.Sort(PersonCollection(collection))
	fmt.Println(collection)
	// desc
	sort.Sort(sort.Reverse(PersonCollection(collection)))
	fmt.Println(collection)
}

Output

[0 1 2 3 4 5 9]
[9 5 4 3 2 1 0]
[a b c d y z]
[z y d c b a]
[{Yi M 2} {Json C 3} {Li L 8} {Zack W 15}]
[{Zack W 15} {Li L 8} {Json C 3} {Yi M 2}]

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buffers

---

Examples of how to allocate a buffer, write in big or little endian format, encode to a hex string, and check if buffers are equal.

Node.js

const buf = Buffer.alloc(6)

let value = 0x1234567890ab
let offset = 0
let byteLength = 6

buf.writeUIntBE(value, offset, byteLength)

let hexstr = buf.toString('hex')
console.log(hexstr)

const buf2 = Buffer.alloc(6)

value = 0x1234567890ab
offset = 0
byteLength = 6

buf2.writeUIntLE(value, offset, byteLength)

hexstr = buf2.toString('hex')
console.log(hexstr)

let isEqual = Buffer.compare(buf, buf2) === 0
console.log(isEqual)

isEqual = Buffer.compare(buf, buf) === 0
console.log(isEqual)

Output

1234567890ab
ab9078563412
false
true

Go

package main

import (
	"bytes"
	"encoding/binary"
	"encoding/hex"
	"fmt"
	"log"
	"math/big"
	"reflect"
)

func writeUIntBE(buffer []byte, value, offset, byteLength int64) {
	slice := make([]byte, byteLength)
	val := new(big.Int)
	val.SetUint64(uint64(value))
	valBytes := val.Bytes()

	buf := bytes.NewBuffer(slice)
	err := binary.Write(buf, binary.BigEndian, &valBytes)
	if err != nil {
		log.Fatal(err)
	}

	slice = buf.Bytes()
	slice = slice[int64(len(slice))-byteLength : len(slice)]

	copy(buffer[offset:], slice)
}

func writeUIntLE(buffer []byte, value, offset, byteLength int64) {
	slice := make([]byte, byteLength)
	val := new(big.Int)
	val.SetUint64(uint64(value))
	valBytes := val.Bytes()

	tmp := make([]byte, len(valBytes))
	for i := range valBytes {
		tmp[i] = valBytes[len(valBytes)-1-i]
	}

	copy(slice, tmp)
	copy(buffer[offset:], slice)
}

func main() {
	buf := make([]byte, 6)
	writeUIntBE(buf, 0x1234567890ab, 0, 6)

	fmt.Println(hex.EncodeToString(buf))

	buf2 := make([]byte, 6)
	writeUIntLE(buf2, 0x1234567890ab, 0, 6)

	fmt.Println(hex.EncodeToString(buf2))

	isEqual := reflect.DeepEqual(buf, buf2)
	fmt.Println(isEqual)

	isEqual = reflect.DeepEqual(buf, buf)
	fmt.Println(isEqual)
}

Output

1234567890ab
ab9078563412
false
true

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maps

---

Node.js

const map = new Map()
map.set('foo', 'bar')

let found = map.has('foo')
console.log(found)

let item = map.get('foo')
console.log(item)

map.delete('foo')

found = map.has('foo')
console.log(found)

item = map.get('foo')
console.log(item)

const map2 = {}
map2['foo'] = 'bar'
item = map2['foo']
delete map2['foo']

const map3 = new Map()
map3.set('foo', 100)
map3.set('bar', 200)
map3.set('baz', 300)

for (let [key, value] of map3) {
  console.log(key, value)
}

Output

true
bar
false
undefined
foo 100
bar 200
baz 300

Go

package main

import "fmt"

func main() {
	map1 := make(map[string]string)

	map1["foo"] = "bar"

	item, found := map1["foo"]
	fmt.Println(found)
	fmt.Println(item)

	delete(map1, "foo")

	item, found = map1["foo"]
	fmt.Println(found)
	fmt.Println(item)

	map2 := make(map[string]int)
	map2["foo"] = 100
	map2["bar"] = 200
	map2["baz"] = 300

	for key, value := range map2 {
		fmt.Println(key, value)
	}
}

Output

true
bar
false

foo 100
bar 200
baz 300

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objects

---

Node.js

const obj = {
  someProperties: {
    'foo': 'bar'
  },
  someMethod: (prop) => {
    return obj.someProperties[prop]
  }
}

let item =  obj.someProperties['foo']
console.log(item)

item = obj.someMethod('foo')
console.log(item)

Output

bar
bar

Go

package main

import "fmt"

type Obj struct {
	SomeProperties map[string]string
}

func NewObj() *Obj {
	return &Obj{
		SomeProperties: map[string]string{
			"foo": "bar",
		},
	}
}

func (o *Obj) SomeMethod(prop string) string {
	return o.SomeProperties[prop]
}

func main() {
	obj := NewObj()

	item := obj.SomeProperties["foo"]
	fmt.Println(item)

	item = obj.SomeMethod("foo")
	fmt.Println(item)
}

Output

bar
bar

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functions

---

Node.js

function add(a, b) {
  return a + b
}

const result = add(2,3)
console.log(result)

Output

5

Go

package main

import "fmt"

func add(a int, b int) int {
	return a + b
}

func main() {
	result := add(2, 3)
	fmt.Println(result)
}

Output

5

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default values

---

Node.js

function greet(name = 'stranger') {
  return `hello ${name}`
}

let message = greet()
console.log(message)

message = greet('bob')
console.log(message)

Output

hello stranger
hello bob

Go

use pointers and check for nil to know if explicitly left blank

package main

import "fmt"

func greet(name *string) string {
	n := "stranger"
	if name != nil {
		n = *name
	}

	return fmt.Sprintf("hello %s", n)
}

func main() {
	message := greet(nil)
	fmt.Println(message)

	name := "bob"
	message = greet(&name)
	fmt.Println(message)
}

Output

hello stranger
hello bob

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destructuring

---

Node.js

const obj = { key: 'foo', value: 'bar' }

const { key, value } = obj
console.log(key, value)

Output

foo bar

Go

package main

import "fmt"

type Obj struct {
	Key   string
	Value string
}

func (o *Obj) Read() (string, string) {
	return o.Key, o.Value
}

func main() {
	obj := Obj{
		Key:   "foo",
		Value: "bar",
	}

	// option 1: multiple variable assignment
	key, value := obj.Key, obj.Value
	fmt.Println(key, value)

	// option 2: return multiple values from a function
	key, value = obj.Read()
	fmt.Println(key, value)
}

Output

foo bar
foo bar

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spread operator

---

Node.js

const array = [1, 2, 3, 4, 5]

console.log(...array)

Output

1 2 3 4 5

Go

package main

import "fmt"

func main() {
	array := []byte{1, 2, 3, 4, 5}

	var i []interface{}
	for _, value := range array {
		i = append(i, value)
	}

	fmt.Println(i...)
}

Output

1 2 3 4 5

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rest operator

---

Node.js

function sum(...nums) {
	let t = 0

	for (let n of nums) {
		t += n
	}

	return t
}

const total = sum(1, 2, 3, 4, 5)
console.log(total)

Output

15

Go

package main

import "fmt"

func sum(nums ...int) int {
	var t int
	for _, n := range nums {
		t += n
	}

	return t
}

func main() {
	total := sum(1, 2, 3, 4, 5)
	fmt.Println(total)
}

Output

15

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swapping

---

Node.js

let a = 'foo'
let b = 'bar'

console.log(a, b);

[b, a] = [a, b]

console.log(a, b)

Output

foo bar
bar foo

Go

package main

import "fmt"

func main() {
	a := "foo"
	b := "bar"

	fmt.Println(a, b)

	b, a = a, b

	fmt.Println(a, b)
}

Output

foo bar
bar foo

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classes

---

Examples of classes, constructors, instantiation, and "this" keyword.

Node.js

class Foo {
  constructor(value) {
    this.item = value
  }

  getItem() {
    return this.item
  }

  setItem(value) {
    this.item = value
  }
}

const foo = new Foo('bar')
console.log(foo.item)

foo.setItem('qux')

const item = foo.getItem()
console.log(item)

Output

bar
qux

Go

(closest thing to a class is to use a structure)

package main

import "fmt"

type Foo struct {
	Item string
}

func NewFoo(value string) *Foo {
	return &Foo{
		Item: value,
	}
}

func (f *Foo) GetItem() string {
	return f.Item
}

func (f *Foo) SetItem(value string) {
	f.Item = value
}

func main() {
	foo := NewFoo("bar")
	fmt.Println(foo.Item)

	foo.SetItem("qux")

	item := foo.GetItem()
	fmt.Println(item)
}

Output

bar
qux

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generators

---

Node.js

function *generator() {
  yield 'hello'
  yield 'world'
}

let gen = generator()

while (true) {
  let { value, done } = gen.next()
  console.log(value, done)

  if (done) {
    break
  }
}

// alternatively
for (let value of generator()) {
  console.log(value)
}

Output

hello false
world false
undefined true
hello
world

Go

package main

import "fmt"

func Generator() chan string {
	c := make(chan string)

	go func() {
		c <- "hello"
		c <- "world"

		close(c)
	}()

	return c
}

func GeneratorFunc() func() (string, bool) {
	s := []string{"hello", "world"}
	i := -1

	return func() (string, bool) {
		i++
		if i >= len(s) {
			return "", false
		}

		return s[i], true
	}
}

func main() {
	gen := Generator()
	for {
		value, more := <-gen
		fmt.Println(value, more)

		if !more {
			break
		}
	}

	// alternatively
	for value := range Generator() {
		fmt.Println(value)
	}

	// alternatively
	genfn := GeneratorFunc()
	for {
		value, more := genfn()
		fmt.Println(value, more)

		if !more {
			break
		}
	}
}

Output

hello true
world true
 false
hello
world
hello true
world true
 false

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datetime

---

Examples of parsing, formatting, and getting unix timestamp of dates.

Node.js

const nowUnix = Date.now()
console.log(nowUnix)

const datestr = '2019-01-17T09:24:23+00:00'
const date = new Date(datestr)
console.log(date.getTime())
console.log(date.toString())

const futureDate = new Date(date)
futureDate.setDate(date.getDate()+14)
console.log(futureDate.toString())

const formatted = `${String(date.getMonth()+1).padStart(2, 0)}/${String(date.getDate()).padStart(2, 0)}/${date.getFullYear()}`
console.log(formatted)

Output

1547718844168
1547717063000
Thu Jan 17 2019 01:24:23 GMT-0800 (Pacific Standard Time)
Thu Jan 31 2019 01:24:23 GMT-0800 (Pacific Standard Time)
01/17/2019

Go

package main

import (
	"fmt"
	"time"
)

func main() {
	nowUnix := time.Now().Unix()
	fmt.Println(nowUnix)

	datestr := "2019-01-17T09:24:23+00:00"
	date, err := time.Parse("2006-01-02T15:04:05Z07:00", datestr)
	if err != nil {
		panic(err)
	}

	fmt.Println(date.Unix())
	fmt.Println(date.String())

	futureDate := date.AddDate(0, 0, 14)
	fmt.Println(futureDate.String())

	formatted := date.Format("01/02/2006")
	fmt.Println(formatted)
}

Output

1547718844
1547717063
2019-01-17 09:24:23 +0000 +0000
2019-01-31 09:24:23 +0000 +0000
01/17/2019

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timeout

---

Node.js

setTimeout(callback, 1e3)

function callback() {
  console.log('called')
}

Output

called

Go

package main

import (
	"fmt"
	"sync"
	"time"
)

var wg sync.WaitGroup

func callback() {
	defer wg.Done()
	fmt.Println("called")
}

func main() {
	wg.Add(1)
	time.AfterFunc(1*time.Second, callback)
	wg.Wait()
}

Output

called

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interval

---

Node.js

let i = 0

const id = setInterval(callback, 1e3)

function callback() {
  console.log('called', i)

  if (i === 3) {
    clearInterval(id)
  }

  i++
}

Output

called 0
called 1
called 2
called 3

Go

package main

import (
	"fmt"
	"time"
)

func callback(i int) {
	fmt.Println("called", i)
}

func main() {
	ticker := time.NewTicker(1 * time.Second)

	i := 0
	for range ticker.C {
		callback(i)

		if i == 3 {
			ticker.Stop()
			break
		}

		i++
	}
}

Output

called 0
called 1
called 2
called 3

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IIFE

---

Immediately invoked function expression

Node.js

(function(name) {
  console.log('hello', name)
})('bob')

Output

hello bob

Go

package main

import "fmt"

func main() {
	func(name string) {
		fmt.Println("hello", name)
	}("bob")
}

Output

hello bob

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files

---

Examples of creating, opening, writing, reading, closing, and deleting files.

Node.js

const fs = require('fs')

// create file
fs.closeSync(fs.openSync('test.txt', 'w'))

// open file (returns file descriptor)
const fd = fs.openSync('test.txt', 'r+')

let wbuf = Buffer.from('hello world.')
let rbuf = Buffer.alloc(12)
let off = 0
let len = 12
let pos = 0

// write file
fs.writeSync(fd, wbuf, pos)

// read file
fs.readSync(fd, rbuf, off, len, pos)

console.log(rbuf.toString())

// close file
fs.closeSync(fd)

// delete file
fs.unlinkSync('test.txt')

Output

hello world.

Go

package main

import (
	"fmt"
	"os"
	"syscall"
)

func main() {
	// create file
	file, err := os.Create("test.txt")
	if err != nil {
		panic(err)
	}

	// close file
	file.Close()

	// open file
	file, err = os.OpenFile("test.txt", os.O_RDWR, 0755)
	if err != nil {
		panic(err)
	}

	// file descriptor
	fd := file.Fd()

	// open file (using file descriptor)
	file = os.NewFile(fd, "test file")

	wbuf := []byte("hello world.")
	rbuf := make([]byte, 12)
	var off int64

	// write file
	if _, err := file.WriteAt(wbuf, off); err != nil {
		panic(err)
	}

	// read file
	if _, err := file.ReadAt(rbuf, off); err != nil {
		panic(err)
	}

	fmt.Println(string(rbuf))

	// close file (using file descriptor)
	if err := syscall.Close(int(fd)); err != nil {
		panic(err)
	}

	// delete file
	if err := os.Remove("test.txt"); err != nil {
		panic(err)
	}
}

Output

hello world.

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json

---

Examples of how to parse (unmarshal) and stringify (marshal) JSON.

Node.js

let jsonstr = '{"foo":"bar"}'

let parsed = JSON.parse(jsonstr)
console.log(parsed)

jsonstr = JSON.stringify(parsed)
console.log(jsonstr)

Output

{ foo: 'bar' }
{"foo":"bar"}

Go

package main

import (
	"encoding/json"
	"fmt"
)

type T struct {
	Foo string `json:"foo"`
}

func main() {
	jsonstr := `{"foo":"bar"}`

	t := new(T)
	err := json.Unmarshal([]byte(jsonstr), t)
	if err != nil {
		panic(err)
	}

	fmt.Println(t)

	marshalled, err := json.Marshal(t)
	jsonstr = string(marshalled)
	fmt.Println(jsonstr)
}

Output

&{bar}
{"foo":"bar"}

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big numbers

---

Examples of creating big number types from and to uint, string, hex, and buffers.

Node.js

let bn = 75n;
console.log(bn.toString(10))

bn = BigInt('75')
console.log(bn.toString(10))

bn = BigInt(0x4b)
console.log(bn.toString(10))

bn = BigInt('0x4b')
console.log(bn.toString(10))

bn = BigInt('0x' + Buffer.from('4b', 'hex').toString('hex'))
console.log(bn.toString(10))
console.log(Number(bn))
console.log(bn.toString(16))
console.log(Buffer.from(bn.toString(16), 'hex'))

let bn2 = BigInt(100)
let isEqual = bn === bn2
console.log(isEqual)

let isGreater = bn > bn2
console.log(isGreater)

let isLesser = bn < bn2
console.log(isLesser)

Output

75
75
75
75
75
75
4b
<Buffer 4b>
false
false
true

Go

package main

import (
	"encoding/hex"
	"fmt"
	"math/big"
)

func main() {
	bn := new(big.Int)
	bn.SetUint64(75)
	fmt.Println(bn.String())

	bn = new(big.Int)
	bn.SetString("75", 10)
	fmt.Println(bn.String())

	bn = new(big.Int)
	bn.SetUint64(0x4b)
	fmt.Println(bn.String())

	bn = new(big.Int)
	bn.SetString("4b", 16)
	fmt.Println(bn.String())

	bn = new(big.Int)
	bn.SetBytes([]byte{0x4b})
	fmt.Println(bn.String())
	fmt.Println(bn.Uint64())
	fmt.Println(hex.EncodeToString(bn.Bytes()))
	fmt.Println(bn.Bytes())

	bn2 := big.NewInt(100)
	isEqual := bn.Cmp(bn2) == 0
	fmt.Println(isEqual)

	isGreater := bn.Cmp(bn2) == 1
	fmt.Println(isGreater)

	isLesser := bn.Cmp(bn2) == -1
	fmt.Println(isLesser)
}

Output

75
75
75
75
75
75
4b
[75]
false
false
true

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promises

---

Node.js

function asyncMethod(value) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve('resolved: ' + value)
    }, 1e3)
  })
}

function main() {
  asyncMethod('foo')
    .then(result => console.log(result))
    .catch(err => console.error(err))

  Promise.all([
    asyncMethod('A'),
    asyncMethod('B'),
    asyncMethod('C')
  ])
  .then(result => console.log(result))
  .catch(err => console.error(err))
}

main()

Output

resolved: foo
[ 'resolved: A', 'resolved: B', 'resolved: C' ]

Go

(closest thing is to use channels)

package main

import (
	"fmt"
	"sync"
	"time"

	"github.com/prometheus/common/log"
)

func asyncMethod(value string) chan interface{} {
	ch := make(chan interface{}, 1)
	go func() {
		time.Sleep(1 * time.Second)
		ch <- "resolved: " + value
		close(ch)
	}()

	return ch
}

func resolveAll(ch ...chan interface{}) chan interface{} {
	var wg sync.WaitGroup
	res := make([]string, len(ch))
	resCh := make(chan interface{}, 1)

	go func() {
		for i, c := range ch {
			wg.Add(1)
			go func(j int, ifcCh chan interface{}) {
				ifc := <-ifcCh
				switch v := ifc.(type) {
				case error:
					resCh <- v
				case string:
					res[j] = v
				}
				wg.Done()
			}(i, c)
		}

		wg.Wait()
		resCh <- res
		close(resCh)
	}()

	return resCh
}

func main() {
	var wg sync.WaitGroup
	wg.Add(2)

	go func() {
		result := <-asyncMethod("foo")
		switch v := result.(type) {
		case string:
			fmt.Println(v)
		case error:
			log.Errorln(v)
		}

		wg.Done()
	}()

	go func() {
		result := <-resolveAll(
			asyncMethod("A"),
			asyncMethod("B"),
			asyncMethod("C"),
		)

		switch v := result.(type) {
		case []string:
			fmt.Println(v)
		case error:
			log.Errorln(v)
		}

		wg.Done()
	}()

	wg.Wait()
}

Output

resolved: foo
[resolved: A resolved: B resolved: C]

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async/await

---

Node.js

function hello(name) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      if (name === 'fail') {
        reject(new Error('failed'))
      } else {
        resolve('hello ' + name)
      }
    }, 1e3)
  })
}

async function main() {
  try {
    let output = await hello('bob')
    console.log(output)

    output = await hello('fail')
    console.log(output)
  } catch(err) {
    console.log(err.message)
  }
}

main()

Output

hello bob
failed

Go

(closest thing is to use channels)

package main

import (
	"errors"
	"fmt"
	"time"

	"github.com/prometheus/common/log"
)

func hello(name string) chan interface{} {
	ch := make(chan interface{}, 1)
	go func() {
		time.Sleep(1 * time.Second)
		if name == "fail" {
			ch <- errors.New("failed")
		} else {
			ch <- "hello " + name
		}
	}()

	return ch
}

func main() {
	result := <-hello("bob")
	switch v := result.(type) {
	case string:
		fmt.Println(v)
	case error:
		log.Errorln(v)
	}

	result = <-hello("fail")
	switch v := result.(type) {
	case string:
		fmt.Println(v)
	case error:
		log.Errorln(v)
	}
}

Output

hello bob
failed

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streams

---

Examples of reading and writing streams

Node.js

const { Readable, Writable } = require('stream')

const inStream = new Readable()

inStream.push(Buffer.from('foo'))
inStream.push(Buffer.from('bar'))
inStream.push(null) // end stream
inStream.pipe(process.stdout)

const outStream = new Writable({
  write(chunk, encoding, callback) {
    console.log('received: ' + chunk.toString('utf8'))
    callback()
  }
})

outStream.write(Buffer.from('abc'))
outStream.write(Buffer.from('xyz'))
outStream.end()

Output

foobar
received: abc
received: xyz

Go

package main

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"os"
	"runtime"
)

func main() {
	inStream := new(bytes.Buffer)
	w := bufio.NewWriter(inStream)
	_, err := w.Write([]byte("foo"))
	if err != nil {
		panic(err)
	}
	_, err = w.Write([]byte("bar"))
	if err != nil {
		panic(err)
	}
	err = w.Flush()
	if err != nil {
		panic(err)
	}

	inStream.WriteTo(os.Stdout)
	fmt.Print("\n")

	outStream := new(bytes.Buffer)
	outStream.Write([]byte("abc\n"))
	outStream.Write([]byte("xyc\n"))
	piper, pipew := io.Pipe()

	go func() {
		sc := bufio.NewScanner(piper)
		for sc.Scan() {
			fmt.Println("received: " + sc.Text())
		}
		if err := sc.Err(); err != nil {
			panic(err)
		}

		os.Exit(0)
	}()

	go func() {
		defer pipew.Close()
		io.Copy(pipew, outStream)
	}()

	defer runtime.Goexit()
}

Output

foobar
received: abc
received: xyc

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event emitter

---

Node.js

const EventEmitter = require('events')
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter()

myEmitter.on('my-event', msg => {
  console.log(msg)
})

myEmitter.on('my-other-event', msg => {
  console.log(msg)
})

myEmitter.emit('my-event', 'hello world')
myEmitter.emit('my-other-event', 'hello other world')

Output

hello world
hello other world

Go

(closest thing is to use channels)

package main

import (
	"fmt"
)

type MyEmitter map[string]chan string

func main() {
	myEmitter := MyEmitter{}
	myEmitter["my-event"] = make(chan string)
	myEmitter["my-other-event"] = make(chan string)

	go func() {
		for {
			select {
			case msg := <-myEmitter["my-event"]:
				fmt.Println(msg)
			case msg := <-myEmitter["my-other-event"]:
				fmt.Println(msg)
			}
		}
	}()

	myEmitter["my-event"] <- "hello world"
	myEmitter["my-other-event"] <- "hello other world"
}

Output

hello world
hello other world

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errors

---

Node.js

const err1 = new Error('some error')

console.log(err1)

class FooError extends Error{
  constructor(message) {
    super(message)
    this.name = 'FooError'
    this.message = message
  }

  toString() {
    return this.message
  }
}

const err2 = new FooError('my custom error')

console.log(err2)

Output

Error: some error
{ FooError: my custom error }

Go

package main

import (
	"errors"
	"fmt"
)

type FooError struct {
	s string
}

func (f *FooError) Error() string {
	return f.s
}

func NewFooError(s string) error {
	return &FooError{s}
}

func main() {
	err1 := errors.New("some error")
	fmt.Println(err1)

	err2 := NewFooError("my custom error")
	fmt.Println(err2)
}

Output

some error
my custom error

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try/catch

---

Node.js

function foo(fail) {
  if (fail) {
    throw Error('my error')
  }
}

function main() {
  try {
    foo(true)
  } catch(err) {
    console.log(`caught error: ${err.message}`)
  }
}

main()

Output

caught error: my error

Go

package main

import (
	"errors"
	"fmt"
)

func foo(fail bool) error {
	if fail {
		return errors.New("my error")
	}

	return nil
}

func main() {
	err := foo(true)
	if err != nil {
		fmt.Printf("caught error: %s\n", err.Error())
	}
}

Output

caught error: my error

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exceptions

---

Node.js

function foo() {
  throw Error('my exception')
}

function main() {
  foo()
}

process.on('uncaughtException', err => {
  console.log(`caught exception: ${err.message}`)
  process.exit(1)
})

main()

Output

caught exception: my exception

Go

package main

import (
	"fmt"
)

func foo() {
	panic("my exception")
}

func main() {
	defer func() {
		if r := recover(); r != nil {
			fmt.Printf("caught exception: %s", r)
		}
	}()

	foo()
}

Output

caught exception: my exception

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regex

---

Node.js

let input = 'foobar'
let replaced = input.replace(/foo(.*)/i, 'qux$1')
console.log(replaced)

let match = /o{2}/i.test(input)
console.log(match)

input = '111-222-333'
let matches = input.match(/([0-9]+)/gi)
console.log(matches)

Output

quxbar
true
[ '111', '222', '333' ]

Go

package main

import (
	"fmt"
	"regexp"
)

func main() {
	input := "foobar"
	re := regexp.MustCompile(`(?i)foo(.*)`)
	replaced := re.ReplaceAllString(input, "qux$1")
	fmt.Println(replaced)

	re = regexp.MustCompile(`(?i)o{2}`)
	match := re.Match([]byte(input))
	fmt.Println(match)

	input = "111-222-333"
	re = regexp.MustCompile(`(?i)([0-9]+)`)
	matches := re.FindAllString(input, -1)
	fmt.Println(matches)
}

Output

quxbar
true
[111 222 333]

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exec (sync)

---

Node.js

const { execSync } = require('child_process')

const output = execSync(`echo 'hello world'`)

console.log(output.toString())

Output

hello world

Go

package main

import (
	"fmt"
	"os/exec"
)

func main() {
	output, err := exec.Command("echo", "hello world").Output()
	if err != nil {
		panic(err)
	}

	fmt.Println(string(output))
}

Output

hello world

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exec (async)

---

Node.js

const { exec } = require('child_process')

exec(`echo 'hello world'`, (error, stdout, stderr) => {
  if (error) {
    console.error(err)
  }

  if (stderr) {
    console.error(stderr)
  }

  if (stdout) {
    console.log(stdout)
  }
})

Output

hello world

Go

package main

import (
	"os"
	"os/exec"
)

func main() {
	cmd := exec.Command("echo", "hello world")
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	cmd.Run()
}

Output

hello world

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tcp server

---

Node.js

const net = require('net')

function handler(socket) {
	socket.write('Received: ')
	socket.pipe(socket)
}

const server = net.createServer(handler)
server.listen(3000)

Output

$ echo 'hello' | nc localhost 3000
Received: hello

Go

package main

import (
	"bufio"
	"net"
)

func handler(conn net.Conn) {
	defer conn.Close()
	reader := bufio.NewReader(conn)

	for {
		message, err := reader.ReadString('\n')
		if err != nil {
			return
		}

		conn.Write([]byte("Received: "))
		conn.Write([]byte(message))
	}
}

func main() {
	listener, err := net.Listen("tcp", ":3000")
	if err != nil {
		panic(err)
	}

	defer listener.Close()

	for {
		conn, err := listener.Accept()
		if err != nil {
			panic(err)
		}

		go handler(conn)
	}
}

Output

$ echo 'hello' | nc localhost 3000
Received: hello

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udp server

---

Node.js

const dgram = require('dgram')
const server = dgram.createSocket('udp4')

server.on('error', err => {
  console.error(err)
  server.close()
})

server.on('message', (msg, rinfo) => {
  const data = msg.toString('utf8').trim()
  console.log(`received: ${data} from ${rinfo.address}:${rinfo.port}`)
})

server.on('listening', () => {
  const address = server.address()
  console.log(`server listening ${address.address}:${address.port}`)
})

server.bind(3000)

Output

$ echo 'hello world' > /dev/udp/0.0.0.0/3000

server listening 0.0.0.0:3000
received: hello world from 127.0.0.1:51452

Go

package main

import (
	"fmt"
	"net"
	"strings"
)

func main() {
	conn, err := net.ListenUDP("udp", &net.UDPAddr{
		Port: 3000,
		IP:   net.ParseIP("0.0.0.0"),
	})
	if err != nil {
		panic(err)
	}

	defer conn.Close()
	fmt.Printf("server listening %s\n", conn.LocalAddr().String())

	for {
		message := make([]byte, 20)
		rlen, remote, err := conn.ReadFromUDP(message[:])
		if err != nil {
			panic(err)
		}

		data := strings.TrimSpace(string(message[:rlen]))
		fmt.Printf("received: %s from %s\n", data, remote)
	}
}

Output

$ echo 'hello world' > /dev/udp/0.0.0.0/3000

server listening [::]:3000
received: hello world from 127.0.0.1:50275

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http server

---

Node.js

const http = require('http')

function handler(request, response) {
  response.writeHead(200, { 'Content-type':'text/plain' })
  response.write('hello world')
  response.end()
}

const server = http.createServer(handler)
server.listen(8080)

Output

$ curl http://localhost:8080
hello world

Go

package main

import (
	"net/http"
)

func handler(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(200)
	w.Write([]byte("hello world"))
}

func main() {
	http.HandleFunc("/", handler)
	if err := http.ListenAndServe(":8080", nil); err != nil {
		panic(err)
	}
}

Output

$ curl http://localhost:8080
hello world

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url parse

---

Node.js

const url = require('url')
const qs = require('querystring')

const urlstr = 'http://bob:[email protected]:8080/somepath?foo=bar'

const parsed = url.parse(urlstr)
console.log(parsed.protocol)
console.log(parsed.auth)
console.log(parsed.port)
console.log(parsed.hostname)
console.log(parsed.pathname)
console.log(qs.parse(parsed.search.substr(1)))

Output

http:
bob:secret
8080
sub.example.com
/somepath
{ foo: 'bar' }

Go

package main

import (
	"fmt"
	"net/url"
)

func main() {
	urlstr := "http://bob:[email protected]:8080/somepath?foo=bar"

	u, err := url.Parse(urlstr)
	if err != nil {
		panic(err)
	}

	fmt.Println(u.Scheme)
	fmt.Println(u.User)
	fmt.Println(u.Port())
	fmt.Println(u.Hostname())
	fmt.Println(u.Path)
	fmt.Println(u.Query())
}

Output

http
bob:secret
8080
sub.example.com
/somepath
map[foo:[bar]]

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gzip

---

Node.js

const zlib = require('zlib')

const data = Buffer.from('hello world', 'utf-8')

zlib.gzip(data, (err, compressed) => {
  if (err) {
    console.error(err)
  }

  console.log(compressed)

  zlib.unzip(compressed, (err, decompressed) => {
    if (err) {
      console.error(err)
    }

    console.log(decompressed.toString())
  })
})

Output

<Buffer 1f 8b 08 00 00 00 00 00 00 13 cb 48 cd c9 c9 57 28 cf 2f ca 49 01 00 85 11 4a 0d 0b 00 00 00>
hello world

Go

package main

import (
	"bytes"
	"compress/gzip"
	"fmt"
)

func main() {
	data := []byte("hello world")

	compressed := new(bytes.Buffer)
	w := gzip.NewWriter(compressed)
	if _, err := w.Write(data); err != nil {
		panic(err)
	}
	if err := w.Close(); err != nil {
		panic(err)
	}

	fmt.Println(compressed.Bytes())

	decompressed := new(bytes.Buffer)
	r, err := gzip.NewReader(compressed)
	if err != nil {
		panic(err)
	}

	_, err = decompressed.ReadFrom(r)
	if err != nil {
		panic(err)
	}

	fmt.Println(string(decompressed.Bytes()))
}

Output

[31 139 8 0 0 0 0 0 0 255 202 72 205 201 201 87 40 207 47 202 73 1 4 0 0 255 255 133 17 74 13 11 0 0 0]
hello world

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dns

---

DNS lookup examples

Node.js

const dns = require('dns')

dns.resolveNs('google.com', (err, ns) => {
  if (err) {
    console.error(err)
  }

  console.log(ns)
})

dns.resolve4('google.com', (err, ips) => {
  if (err) {
    console.error(err)
  }

  console.log(ips)
})

dns.resolveMx('google.com', (err, mx) => {
  if (err) {
    console.error(err)
  }

  console.log(mx)
})

dns.resolveTxt('google.com', (err, txt) => {
  if (err) {
    console.error(err)
  }

  console.log(txt)
})

dns.setServers(['1.1.1.1'])
console.log(dns.getServers())

dns.resolveNs('google.com', (err, ns) => {
  if (err) {
    console.error(err)
  }

  console.log(ns)
})

Output

[
  'ns2.google.com',
  'ns3.google.com',
  'ns4.google.com',
  'ns1.google.com'
]
[ '172.217.11.78' ]
[ { exchange: 'alt4.aspmx.l.google.com', priority: 50 },
  { exchange: 'alt2.aspmx.l.google.com', priority: 30 },
  { exchange: 'alt3.aspmx.l.google.com', priority: 40 },
  { exchange: 'aspmx.l.google.com', priority: 10 },
  { exchange: 'alt1.aspmx.l.google.com', priority: 20 } ]
[ [ 'v=spf1 include:_spf.google.com ~all' ],
  [ 'docusign=05958488-4752-4ef2-95eb-aa7ba8a3bd0e' ],
  [ 'facebook-domain-verification=22rm551cu4k0ab0bxsw536tlds4h95' ],
  [ 'globalsign-smime-dv=CDYX+XFHUw2wml6/Gb8+59BsH31KzUr6c1l2BPvqKX8=' ] ]
[ '1.1.1.1' ]
[
  'ns1.google.com',
  'ns2.google.com',
  'ns4.google.com',
  'ns3.google.com'
]

Go

package main

import (
	"fmt"
	"net"
)

func main() {
	ns, err := net.LookupNS("google.com")
	if err != nil {
		panic(err)
	}

	fmt.Printf("%s\n", ns)

	ips, err := net.LookupIP("google.com")
	if err != nil {
		panic(err)
	}

	fmt.Println(ips)

	mx, err := net.LookupMX("google.com")
	if err != nil {
		panic(err)
	}

	fmt.Println(mx)

	txt, err := net.LookupTXT("google.com")
	if err != nil {
		panic(err)
	}

	fmt.Println(txt)

	r := &net.Resolver{
		PreferGo: true,
		Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
			d := net.Dialer{
				Timeout: time.Millisecond * time.Duration(10_000),
			}
			return d.DialContext(ctx, "udp", "1.1.1.1:53")
		},
	}

	ns, _ = r.LookupNS(context.Background(), "google.com")
	fmt.Printf("%s", ns)
}

Output

[%!s(*net.NS=&{ns3.google.com.}) %!s(*net.NS=&{ns4.google.com.}) %!s(*net.NS=&{ns1.google.com.}) %!s(*net.NS=&{ns2.google.com.})]
[172.217.5.78 2607:f8b0:4007:80d::200e]
[0xc0000ba2e0 0xc0000ba260 0xc0000ba2a0 0xc0000ba280 0xc0000ba300]
[facebook-domain-verification=22rm551cu4k0ab0bxsw536tlds4h95 docusign=05958488-4752-4ef2-95eb-aa7ba8a3bd0e v=spf1 include:_spf.google.com ~all globalsign-smime-dv=CDYX+XFHUw2wml6/Gb8+59BsH31KzUr6c1l2BPvqKX8=]
[%!s(*net.NS=&{ns2.google.com.}) %!s(*net.NS=&{ns1.google.com.}) %!s(*net.NS=&{ns3.google.com.}) %!s(*net.NS=&{ns4.google.com.})]

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crypto

---

Node.js

const crypto = require('crypto')

const hash = crypto.createHash('sha256').update(Buffer.from('hello')).digest()

console.log(hash.toString('hex'))

Output

2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824

Go

package main

import (
	"crypto/sha256"
	"encoding/hex"
	"fmt"
)

func main() {
	hash := sha256.Sum256([]byte("hello"))

	fmt.Println(hex.EncodeToString(hash[:]))
}

Output

2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824

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env vars

---

Node.js

const key = process.env['API_KEY']

console.log(key)

Output

$ API_KEY=foobar node examples/env_vars.js
foobar

Go

package main

import (
	"fmt"
	"os"
)

func main() {
	key := os.Getenv("API_KEY")

	fmt.Println(key)
}

Output

$ API_KEY=foobar go run examples/env_vars.go
foobar

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cli args

---

Node.js

const args = process.argv.slice(2)

console.log(args)

Output

$ node examples/cli_args.js foo bar qux
[ 'foo', 'bar', 'qux' ]

Go

package main

import (
	"fmt"
	"os"
)

func main() {
	args := os.Args[1:]
	fmt.Println(args)
}

Output

$ go run examples/cli_args.go foo bar qux
[foo bar qux]

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cli flags

---

Node.js

const yargs = require('yargs')

const { foo='default value', qux=false } = yargs.argv
console.log('foo:', foo)
console.log('qux:', qux)

Output

$ node examples/cli_flags.js --foo='bar' --qux=true
foo: bar
qux: true

Go

package main

import (
	"flag"
	"fmt"
)

func main() {
	var foo string
	flag.StringVar(&foo, "foo", "default value", "a string var")

	var qux bool
	flag.BoolVar(&qux, "qux", false, "a bool var")

	flag.Parse()

	fmt.Println("foo:", foo)
	fmt.Println("qux:", qux)
}

Output

$ go run examples/cli_flags.go -foo='bar' -qux=true
foo: bar
qux: true

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stdout

---

Node.js

process.stdout.write('hello world\n')

Output

hello world

Go

package main

import (
	"fmt"
	"os"
)

func main() {
	fmt.Fprint(os.Stdout, "hello world\n")
}

Output

hello world

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stderr

---

Node.js

process.stderr.write('hello error\n')

Output

hello error

Go

package main

import (
	"fmt"
	"os"
)

func main() {
	fmt.Fprint(os.Stderr, "hello error\n")
}

Output

hello error

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stdin

---

Node.js

const stdin = process.openStdin()

process.stdout.write('Enter name: ')

stdin.addListener('data', text => {
  const name = text.toString().trim()
  console.log('Your name is: ' + name)

  stdin.pause()
})

Output

Enter name: bob
Your name is: bob

Go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strings"
)

func main() {
	reader := bufio.NewReader(os.Stdin)
	fmt.Print("Enter name: ")

	text, err := reader.ReadString('\n')
	if err != nil {
		panic(err)
	}

	name := strings.TrimSpace(text)
	fmt.Printf("Your name is: %s\n", name)
}

Output

Enter name: bob
Your name is: bob

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modules

---

Node.js

# initializing metadata and dependencies file (package.json)
$ npm init

# installing a module
$ npm install moment --save

# updating a module
$ npm install moment@latest --save

# removing a module
$ npm uninstall moment --save

# pruning modules (removing unused modules)
$ npm prune

# publishing a module
$ npm publish

// importing a module
const moment = require('moment')

const now = moment().unix()
console.log(now)

Output

1546595748

// exporting a module
module.exports = {
  greet(name) {
    console.log(`hello ${name}`)
  }
}

// importing exported module
const greeter = require('./greeter')

greeter.greet('bob')

Output

hello bob

Go

Setup

# enable Go modules support
GO111MODULE=on

# initializing dependencies file (go.mod)
$ go mod init

# installing a module
$ go get github.com/go-shadow/moment

# updating a module
$ go get -u github.com/go-shadow/moment

# removing a module
$ rm -rf $GOPATH/pkg/mod/github.com/go-shadow/moment@v<tag>-<checksum>/

# pruning modules (removing unused modules from dependencies file)
$ go mod tidy

# download modules being used to local vendor directory (equivalent of downloading node_modules locally)
$ go mod vendor

# publishing a module:
# Note: Go doesn't have an index of repositories like NPM.
# Go modules are hosted as public git repositories.
# To publish, simply push to the repository and tag releases.

package main

import (
	"fmt"

	// importing a module
	"github.com/go-shadow/moment"
)

func main() {
	now := moment.New().Now().Unix()
	fmt.Println(now)
}

Output

1546595748

package greeter

import (
	"fmt"
)

// exporting a module (use a capitalized name to export function)
func Greet(name string) {
	fmt.Printf("hello %s", name)
}

package main

import (
	// importing exported module
	greeter "github.com/miguelmota/golang-for-nodejs-developers/examples/greeter_go"
)

func main() {
	greeter.Greet("bob")
}

Output

hello bob

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stack trace

---

Node.js

function foo() {
  throw new Error('failed')
}

try {
  foo()
} catch(err) {
  console.trace(err)
}

Output

Trace: Error: failed
    at foo (/Users/bob/examples/stack_trace.js:2:9)
    at Object.<anonymous> (/Users/bob/examples/stack_trace.js:6:3)
    at Module._compile (internal/modules/cjs/loader.js:688:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:699:10)
    at Module.load (internal/modules/cjs/loader.js:598:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:537:12)
    at Function.Module._load (internal/modules/cjs/loader.js:529:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:741:12)
    at startup (internal/bootstrap/node.js:285:19)
    at bootstrapNodeJSCore (internal/bootstrap/node.js:739:3)
    at Object.<anonymous> (/Users/bob/examples/stack_trace.js:8:11)
    at Module._compile (internal/modules/cjs/loader.js:688:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:699:10)
    at Module.load (internal/modules/cjs/loader.js:598:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:537:12)
    at Function.Module._load (internal/modules/cjs/loader.js:529:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:741:12)
    at startup (internal/bootstrap/node.js:285:19)
    at bootstrapNodeJSCore (internal/bootstrap/node.js:739:3)

Go

package main

import (
	"errors"
	"fmt"
	"runtime/debug"
)

func foo() {
	panic(errors.New("failed"))
}

func main() {
	defer func() {
		if r := recover(); r != nil {
			fmt.Println(string(debug.Stack()))
		}
	}()

	foo()
}

Output

goroutine 1 [running]:
runtime/debug.Stack(0xc000090eb8, 0x10a8400, 0xc00007e1c0)
        /Users/mota/.gvm/gos/go1.11/src/runtime/debug/stack.go:24 +0xa7
main.main.func1()
        /Users/bob/examples/stack_trace.go:16 +0x46
panic(0x10a8400, 0xc00007e1c0)
        /Users/mota/.gvm/gos/go1.11/src/runtime/panic.go:513 +0x1b9
main.foo(...)
        /Users/bob/examples/stack_trace.go:10
main.main()
        /Users/bob/examples/stack_trace.go:20 +0xa2

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databases

---

Example of creating a table, inserting rows, and reading rows from a sqlite3 database

Node.js

const sqlite3 = require('sqlite3').verbose()
const db = new sqlite3.Database('./sqlite3.db')

db.serialize(() => {
  db.run('CREATE TABLE persons (name TEXT)')

  const stmt = db.prepare('INSERT INTO persons VALUES (?)')
  const names = ['alice', 'bob', 'charlie']
  for (let i = 0; i < names.length; i++) {
    stmt.run(names[i])
  }

  stmt.finalize()

  db.each('SELECT rowid AS id, name FROM persons', (err, row) => {
    if (err) {
      console.error(err)
      return
    }

    console.log(row.id, row.name)
  })
})

db.close()

Output

1 'alice'
2 'bob'
3 'charlie'

Go

package main

import (
	"database/sql"
	"fmt"

	_ "github.com/mattn/go-sqlite3"
)

func main() {
	db, err := sql.Open("sqlite3", "./sqlite3.db")
	if err != nil {
		panic(err)
	}
	defer db.Close()

	_, err = db.Exec("CREATE TABLE persons (name TEXT)")
	if err != nil {
		panic(err)
	}

	tx, err := db.Begin()
	if err != nil {
		panic(err)
	}

	stmt, err := tx.Prepare("INSERT INTO persons VALUES (?)")
	if err != nil {
		panic(err)
	}
	defer stmt.Close()

	names := []string{"alice", "bob", "charlie"}

	for _, name := range names {
		_, err := stmt.Exec(name)
		if err != nil {
			panic(err)
		}
	}
	tx.Commit()

	rows, err := db.Query("SELECT rowid AS id, name FROM persons")
	if err != nil {
		panic(err)
	}
	defer rows.Close()

	for rows.Next() {
		var id int
		var name string
		err = rows.Scan(&id, &name)
		if err != nil {
			panic(err)
		}
		fmt.Println(id, name)
	}

	err = rows.Err()
	if err != nil {
		panic(err)
	}
}

Output

1 alice
2 bob
3 charlie

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testing

---

Node.js

const test = require('tape')

test(t => {
  const tt = [
		{a:1, b:1, ret:2},
		{a:2, b:3, ret:5},
		{a:5, b:5, ret:10}
  ]

  t.plan(tt.length)

  tt.forEach(tt => {
    t.equal(sum(tt.a, tt.b), tt.ret)
  })
})

function sum(a, b) {
	return a + b
}

Output

$ node examples/example_test.js
TAP version 13
# (anonymous)
ok 1 should be equal
ok 2 should be equal
ok 3 should be equal

1..3
# tests 3
# pass  3

# ok

Go

package example

import (
	"fmt"
	"testing"
)

func TestSum(t *testing.T) {
	for _, tt := range []struct {
		a   int
		b   int
		ret int
	}{
		{1, 1, 2},
		{2, 3, 5},
		{5, 5, 10},
	} {
		t.Run(fmt.Sprintf("(%v + %v)", tt.a, tt.b), func(t *testing.T) {
			ret := sum(tt.a, tt.b)
			if ret != tt.ret {
				t.Errorf("want %v, got %v", tt.ret, ret)
			}
		})
	}
}

func sum(a, b int) int {
	return a + b
}

Output

$ go test -v examples/example_test.go
=== RUN   TestSum
=== RUN   TestSum/(1_+_1)
=== RUN   TestSum/(2_+_3)
=== RUN   TestSum/(5_+_5)
--- PASS: TestSum (0.00s)
    --- PASS: TestSum/(1_+_1) (0.00s)
    --- PASS: TestSum/(2_+_3) (0.00s)
    --- PASS: TestSum/(5_+_5) (0.00s)
PASS
ok      command-line-arguments  0.008s

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benchmarking

---

Node.js

const Benchmark = require('benchmark')

const suite = new Benchmark.Suite
suite.add('fib#recursion', () => {
  fibRec(10)
})
.add('fib#loop', () => {
  fibLoop(10)
})
.on('complete', () => {
  console.log(suite[0].toString())
  console.log(suite[1].toString())
})
.run({
  async: true
})

function fibRec(n) {
  if (n <= 1) {
    return n
  }

  return fibRec(n-1) + fibRec(n-2)
}

function fibLoop(n) {
  let f = [0, 1]
  for (let i = 2; i <= n; i++) {
    f[i] = f[i-1] + f[i-2]
  }
  return f[n]
}

Output

$ node examples/benchmark_test.js
fib#recursion x 1,343,074 ops/sec ±1.26% (84 runs sampled)
fib#loop x 20,104,517 ops/sec ±3.78% (78 runs sampled)

Go

package example

import (
	"testing"
)

func BenchmarkFibRec(b *testing.B) {
	for n := 0; n < b.N; n++ {
		fibRec(10)
	}
}

func BenchmarkFibLoop(b *testing.B) {
	for n := 0; n < b.N; n++ {
		fibLoop(10)
	}
}

func fibRec(n int) int {
	if n <= 1 {
		return n
	}

	return fibRec(n-1) + fibRec(n-2)
}

func fibLoop(n int) int {
	f := make([]int, n+1, n+2)
	if n < 2 {
		f = f[0:2]
	}
	f[0] = 0
	f[1] = 1
	for i := 2; i <= n; i++ {
		f[i] = f[i-1] + f[i-2]
	}
	return f[n]
}

Output

$ go test -v -bench=. -benchmem examples/benchmark_test.go
goos: darwin
goarch: amd64
BenchmarkFibRec-8        5000000               340 ns/op               0 B/op          0 allocs/op
BenchmarkFibLoop-8      30000000                46.5 ns/op            96 B/op          1 allocs/op
PASS
ok      command-line-arguments  3.502s

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documentation

---

Node.js

jsdoc

/**
 * Creates a new Person.
 * @class
 * @example
 * const person = new Person('bob')
 */
class Person {
  /**
   * Create a person.
   * @param {string} [name] - The person's name.
   */
  constructor(name) {
    this.name = name
  }

  /**
   * Get the person's name.
   * @return {string} The person's name
   * @example
   * person.getName()
   */
  getName() {
    return this.name
  }

  /**
   * Set the person's name.
   * @param {string} name - The person's name.
   * @example
   * person.setName('bob')
   */
  setName(name) {
    this.name = name
  }
}

Go

godoc

person.go

package person

import "fmt"

// Person is the structure of a person
type Person struct {
	name string
}

// NewPerson creates a new person. Takes in a name argument.
func NewPerson(name string) *Person {
	return &Person{
		name: name,
	}
}

// GetName returns the person's name
func (p *Person) GetName() string {
	return p.name
}

// SetName sets the person's name
func (p *Person) SetName(name string) string {
	return p.name
}

person_test.go

// Example of creating a new Person.
func ExampleNewPerson() {
	person := NewPerson("bob")
	_ = person
}

// Example of getting person's name.
func ExamplePerson_GetName() {
	person := NewPerson("bob")
	fmt.Println(person.GetName())
	// Output: bob
}

// Example of setting person's name.
func ExamplePerson_SetName() {
	person := NewPerson("alice")
	person.SetName("bob")
}

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Contributing

Pull requests are welcome!

Please submit a pull request for new interesting additions or for general content fixes.

If updating code, update both the README and the code in the examples folder.

License

Released under the MIT license.

© Miguel Mota