typescript.md

TypeScript Cheatsheet

Variables & constants

C

int a;
int b = 42;
#define C 42

TS

let a: number;
let b = 42; // type inference
const c = 42; // mostly do this

Printing

C

#include <stdio.h>

printf("%d\n", 42);
printf("%s\n", "foo");

TS

console.log(42);
console.log('foo');

Types

Numbers

C

int a;
float b;
// ...

a = 42;
b = 4.2;

TS

let a: number;

a = 42;
a = 4.2;

Strings

C

char a;
char *b;

a = 'f';
b = "foo";

TS

let a: string;

a = 'f';
a = "f";
a = 'foo';
a = "foo";

C

char *a = "foo";
strlen(a); // 3

TS

let a = 'foo';
a.length; // 3

Template strings

C

#include <stdio.h>

int a = 49;
printf("I love %d\n", a);

TS

const a = 49;
console.log(`I love ${a}`);

// not for only printing
b = `I love ${a}`;

Booleans

C

#include <stdbool.h>
bool a = true;

TS

const a: boolean = true;
const b = true; // type inference

Conditionals

C

if (1 + 1 == 2) {
	// ...
}

TS

// bad
if (1 + 1 == 2) {
	// ...
}

// good (does type check)
if (1 + 1 === 2) {
	// ...
}

C

int a = 1;
int b = 2;
int max = a > b ? a : b; // 2

TS

const a = 1;
const b = 2;
const max = a > b ? a : b; // 2

Functions

C

int triple(int n) {
	return n * 3;
}

TS

const triple1 = (n: number): number => {
	return n * 3;
}

// type inference
const triple2 = (n: number) => {
	return n * 3;
}

// only for single-line functions
const triple3 = (n: number) => n * 3;

More types

Type aliases

C

typedef int MyType;
MyType a;

TS

type MyType = number;
let a: MyType;

Objects

C

struct Course {
	char *name;
	int students;
}

Course cs1511 = {
	'Programming Fundamentals',
	893
};

TS

type Course = {
	name: string;
	students: number;
}

// could also use type inference
let cs1511: Course = {
	name: 'Programming Fundamentals',
	students: 893
}

Arrays

C

int a[3] = {1, 2, 3};

a[42] = 4; // segmentation fault

TS

const a: number[] = [1, 2, 3];

a[42] = 4;
a; // [1, 2, 3, 4]

C

int a[3] = {1, 2, 3};

int i = 0;
while (i < 3) {
	int n = a[i];
	printf("%d\n", n);
	i++;
}

TS

const a: number[] = [1, 2, 3];

let i = 0;
while (i < 3) {
	const n = a[i];
	console.log(n);
	i++;
}

// preferred
a.forEach((n) => {
	console.log(n);
});

C

int a[3] = {1, 2, 3};

int i = 0;
while (i < 3) {
	a[i] = a[i] * 2;
	i++;
}

a; // {2, 4, 6}

TS

const a: number[] = [1, 2, 3];
const a2 = a.map((n) => n * 2);

a;  // [1, 2, 3]
a2; // [2, 4, 6]

Union types

TS

let a: number | string;
a = 42;
a = 'foo';

let b = 'foo' | 'bar';
b = 'foo';
b = 'bar';
b = 'baz'; // compile error

Undefined & null

TS

let a: number;
console.log(a); // undefined

let b: number | null;
b = 42;
b = null; // the "nothing" type