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JavaScript.language.txt
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JavaScript.language.txt
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JAVASCRIPT
VERSION ==> #Standard is called ECMAScript. JavaScript and ActionScript are dialects.
#This doc shows strict mode only
SUPPORT ==> #Use this notation for new features:
~# - stage 3 proposal
NUM*# - introduced by Node NUM.*.*
*# - not latest Node
-# - not all supported web browsers
|# - a core Babel plugin exists (only documented if lacks Node/browser support)
||# - a non-core Babel plugin exists
|||# - a polyfill/ponyfill exists
#Only document|use features in stage >= 3
#Can look at support with:
# - EcmaScript kangax compat-table
# - http://node.green/
MAIN PRINCIPLES ==> #Case-sensitive. Whitespaces are ignored.
#Type: weak, dynamic, generic, late/duck.
#Lexical-scope
#Functional (first-class functions)
#Object-oriented (prototype-based)
#Imperative (structures close to C)
#Need a host environnement (e.g. browser) for I/O
#Memory management: garbage collection.
EXECUTION ==> #Each browser has own JavaScript engine, which was in the past interpreted,
#but now is byte-compiled or compiled:
# - V8 (Chrome, Opera 15+, Edge >=2020, Node.js, Deno)
# - SpiderMonkey (Firefox, MongoDB >=3.2)
# - JavaScriptCore/SquirrelFish/Nitro (Safari) part of WebKit
# - Chakra (IE9+, Edge <2019), opensourced at ChakraCore
/=+===============================+=\
/ : : \
)==: ASYNC :==(
\ :_______________________________: /
\=+===============================+=/
EVENT LOOP ==> #Loops:
# - each event loop loops through [macro]tasks
# - each macrotask loops through microtasks|tick
# - each microtask is run synchronously
NEW TASKS ==> #Each thread has a single event loop
# - creates a new thread: process, WebWorker, cross-origin <iframe>
#Macrotasks are created by I/O code, which includes:
# - setTimeout|Interval|Immediate()
# - filesystem, network or OS calls
# - not streams on their own
# - event handlers triggered by browser interaction.
# - events triggered directly through JavaScript, which include Node.js EVENTEMITTER, are sync.
#Microtasks are created by:
# - process.nextTick()
# - queueMicrotask()
# - PROMISE.then|catch() callbacks
# - priority:
# - first-in first-out
# - process.nextTick() before other types of microtasks
# - e.g. if a process.nextTick() create a new process.nextTick(),
# it will be fired before pending PROMISE microtasks
PERFORMANCE ==> #For Node.js:
# - minimal time of a macrotask is 1ms.
# I.e. a macrotask that only does setTimeout(..., 0) will last 1ms
# - there is no minimal time for a microtask
SINGLE-THREADED ==> #Each event loop is single-threaded:
# - i.e. only one microtask and one macrotask runs at any time
#Resources:
# - I/O-intensive tasks:
# - are the slowest
# - should yield the thread and be woken up on a new macrotask
# - this is what most I/O functions do by default, i.e. I/O calls are
# optimally handled
# - i.e. developer just need to use async I/O functions
# - CPU-intensive tasks:
# - will hold the whole thread
# - if too slow, should spawn a new thread instead
# - memory consumption:
# - is very low, because thread and processes is what makes memory go high
ASYNC EXPECTATION ==> #Libraries exposing callbacks should trigger them in a new microtask,
#because this what consumers usually expect.
# - e.g. this would otherwise be problematic:
# let VAR = FUNC(CALLBACK); VAR.on('start', ...)
THREAD EXIT ==> #Thread exits when the event loop has no more macrotasks
#In a browser, this never happens, as there are always DOM event listeners.
#In Node.js:
# - timers methods keep the thread alive
# - i.e. automatically ref'd
# - process.nextTick(), queueMicrotask(), setTimeout|setInterval()
# - PROMISEs do not keep the thread alive by themselves
# - PROMISE.then|catch() FUNC, await PROMISE
# - but they do when the PROMISE relies on ref'd logic
# - any external input is ref'd by Node.js
# - I/O, processes, network
# - sometimes ref|unref() methods are exposed to manually control this
ASYNC STACK TRACE ==> #Also called "long stack trace"
#When using async, the callback function does not include stack trace from parent function
# - because it is processed on a different microtask
#This is missing in:
# - setTimeout|Interval|Immediate(FUNC), process.nextTick(FUNC), queueMicrotask()
# - filesystem, network, OS or browser interaction event handlers
# - new Promise()
#This is not missing when using async|await:
# - including whn using Promise.*()
# - supported:
# - code during|before an await statement: always
# - code after an await statement: most browsers and Node
/=+===============================+=\
/ : : \
)==: SCOPE :==(
\ :_______________________________: /
\=+===============================+=/
GENERAL ==> # - variable scope is:
# - "var": FUNC {...}
-|# - "let|const": any {...}
# - any function inherits scope of the function in which it is declared (not called)
# - inherits by reference, not by value
globalThis -|#Global scope reference
-|#Otherwise can be in many places (self in WORKER, window in DOM, global in Node.js, this otherwise)
DECLARATION ==> # - using undeclared VAR throws ReferenceError (except with typeof)
# - using VAR (even if declared in parent scope) declared later in
# current scope with:
-|# - "let|const": throws ReferenceError ("Temporal Dead Zone")
# - "var": adds an implicit empty declaration before, i.e. will be
# undefined (variable hoisting)
# - function FUNC(){}: adds an implicit declaration+assignment before
DECLARING FUNCTIONS ==> # - FUNC = function [FUNC2](){}
# - declared+assigned at runtime (like other variables)
# - this also covers anonymous function, and void function [FUNC2](){}
# - Using "FUNC2":
# - equivalent of doing let FUNC2 = function(){} at the beginning of
# the same function
# - allow recursion to reference themselves without risk of parent
# scope to reassign FUNC2
# - function FUNC2(){}:
# - declared+assigned at parsetime
# - i.e. equivalent of doing let FUNC2 = function () {} at {...} scope
# beginning
# - new Function(...): child of global scope
MEMORY MANAGEMENT ==> #Garbage collection:
# - use tracing, i.e. no problem with reference cycles
# - root objects are global variables
# - closures carry references to their parent scope, but only of the
# references they use
# - this might be problematic when closures are returned, i.e. go up the
# stack, extending their parent scope lifetime
#Memory leak happens with combination of variables being:
# - big, e.g.:
# - functions carrying parent SCOPEs
# - big objects
# - raw data returned from server
# - long-lived, e.g.:
# - attached to top/long-lived SCOPEs, e.g. global variables, e.g.:
# - long-lived DOM elements
# - global functions (e.g. global event handlers, setInterval(), ...)
#Avoiding:
# - unset variables just after being used if they are big or attached to
# long-lived objects
# - "unset": prefer setting empty value than using "delete"
# - only use closures as argument or return value when needed
new WeakRef(OBJ) #Keep a reference to OBJ, without preventing OBJ from being GC'd
#Should not rely:
# - on when|whether GC happens, since this is very variable
# - on it to guess when|whether GC happens
#For example, should not be used for resource cleanup.
#Should only be used as a way to prevent increasing memory usage.
# - e.g. caches or weak maps
# - consider using WeakMap|WeakSet if possible
WEAKREF.deref()->OBJ|undefined #Returns OBJ. undefined if OBJ was GC'd
new FinalizationRegistry(FUNC(OBJ, VAL)) #Same improper use warnings as WeakRef
FINALIZATION_REGISTRY.register #Calls FUNC(OBJ, VAL) when OBJ is GC'd
(OBJ[, VAL][, VAL2]) #Keeps weak reference to OBJ|VAL2 (does not prevent it from being GC'd)
#Keep strong reference to VAL (i.e. should not be OBJ)
#VAL2 is the one to use with unregister() (can be same as OBJ)
FINALIZATION_REGISTRY.unregister
(VAL2)->BOOL #BOOL is whether it was registered
new ShadowRealm() 18.13.0*-|~#Global environment
--experimental-shadow-realm <18.13.0*-|~#
SVAL 18.13.0*-|~#Cannot be an OBJ, except for a FUNC providing it does not use OBJ as argument or return value
REALM.importValue('MDL', 'VAR')
->PROMISE_SVAL 18.13.0*-|~#Like (await import('MDL')).VAR but bound to a REALM
REALM.evaluate('CODE')->SVAL 18.13.0*-|~#Like eval('CODE') but bound to a REALM
18.13.0*-|~#Each call has its own scope, but share the same global scope
/=+===============================+=\
/ : : \
)==: BASIC STATEMENTS :==(
\ :_______________________________: /
\=+===============================+=/
RESERVED WORDS ==> #enum, await, implements, package, protected, public, private, interface,
#static
STATEMENT; #; optional, but recommended in case could be interpreted as multiline
STATEMENT\ #Only required for multiline statements:
# - within a STR
# - if first line could be interpreted as standalone statement.
// COMMENT
/* COMMENT */ #
#!... #Ignored if first non-blank line
"use strict"; #Start strict mode:
# - i.e. strict ES6|ES7 conformance
# - allows faster optimization by browsers
# - not compatible until IE10
#Applies to current and child scopes:
# - child scopes: including nested functions, anonymous functions, eval(),
# new Function(), etc.
# - but not functions declared in different scopes and called in current|child scopes
# - warning: concatenating with other scripts might put them in same scope,
# making them strict too.
# - must be before any statement (otherwise noop)
#Implicit in any ES6 module (i.e. useless), but not in Node.js modules or
#global scripts
#In the web console, can use an anonymous function in order to use strict mode.
QUAL VAR[ = VAL] #Declaration. Default value is undefined.
[, VAR2[ = VAL2]]... #VAR:
# - cannot be a reserved keyword
# - can contain:
# - $
# - any Unicode char with property "ID_Continue":
# - letters-like
# - numbers-like
# - diacretics
# - _
# - U+200C U+200D (zero-width space)
# - can be included as is, or using \u.... or \u{....}
# - first character must be Unicode char with property "ID_Start",
# (i.e. only letters-like) or $ or _
VAR = VAL; #Assignation.
#Returns VAL, so chain possible: VAR = VAR2 = VAL, but means VAR2 is global
[QUAL] [VAR [= VAL],...[, ...ITERABLE2]] -|#[QUAL ]VAR = ITERABLE[NUM], ...
= ITERABLE -|#VAL is default value
-|#ITERABLE2 is variadic assignment
[QUAL] { KEY: VAR[ = VAL] } = OBJ -|#[QUAL ]VAR = OBJ[KEY], ...
-|#Without 'QUAL', must wrap with ({...} = OBJ)
-|#VAL is default value
-|#Can be { KEY: { KEY2: ... } }
-|#KEY can appear several times with different VAR,
-|#including { KEY: { KEY2 }, KEY: KEY }
[QUAL] { KEY[ = VAL] } = OBJ -|#Same as QUAL { KEY: KEY[ = VAL] } = OBJ
QUAL #var|let|const|using
let VAR -|#Like var VAR, but {} block scoped.
const VAR -|#Like let VAR but read-only, i.e. throws error on assignments beyond
-|#declaration
-|#Is shallow: if OBJ, only OBJ is read-only, not OBJ.VAR
-|#Is only for current block scope since:
-|# - function arguments imply new assignment
-|# - function return value must be assigned to be used as reference
delete OBJ.VAR #Like assigning undefined except:
# - remove key as well
# - cannot be performed if non-configurable
# - can be performed if non-writable
#Note: for ARR[NUM], does not modify length (like assigning undefined)
#Returns true if OBJ (not OBJ.VAR) exists.
void STATEMENT #Same as STATEMENT, but returns undefined
#void 0 is sometimes used to return undefined without risk for shadowing
# - But not needed since shadowing can be caught by linting
eval("STATEMENT...") #Fire STATEMENT... in current scope. Return last STATEMENT return value.
#To avoid.
#If argument non STR, renvoie VAL.
#"VAR = VAL" does not declare anything.
#Can throw SyntaxError or EvalError.
/=+===============================+=\
/ : : \
)==: STRUCTURES :==(
\ :_______________________________: /
\=+===============================+=/
SINGLE LINE ==> #Block braces can be skipped if only on single next line (to avoid)
VAL #Anything that returns a VAL
EXPR #Anything that could go on a single line of code ending with ;
... #Several EXPR
TEST ? VAL1 : VAL2 #Returns VAL1 or VAL2
VAL && VAL2 #Same as VAL ? VAL : VAL2
VAL || VAL2 #Same as VAL ? VAL2 : VAL
VAL ?? VAL2 #Same as VAL == null ? VAL : VAL2
VAR &&= VAL2 #Same as VAR = VAR && VAL2
VAR ||= VAL2 #Same as VAR = VAR || VAL2
VAR ??= VAL2 #Same as VAR = VAR ?? VAL2
VAL1, VAL2 #Evaluates both, but returns VAL2.
#Use case: in for or while loops.
{ ... } #Creates a scope
(VAL) #To increase precedence.
if ( TEST ) { ... }
[else if ( TEST ) { ... }]...
[else { ... }]
switch (VAL) { #Use VAL === VAL2
case VAL2: ... [break;] ... #If no break, execute next case (including "default")
case VAL3: case VAL4: ... [break;] ... #Case can be empty, meaning several "case" match when any matches.
[default: ... [break;]] #... can be wrapped in { ... }, which creates a scope
}
for ( [EXPR1] ; [TEST] ; [EXPR2] ) { ... } #Same as:
# EXPR1; while ( TEST ) { ...; EXPR2; }
while ( TEST ) { ... }
do { ... } while ( TEST )
for ( [QUAL] VAR in OBJ ) { ... } #Iterate over keys that are enumerable, excluding SYMs
#OBJ can be ITERATOR.
break [LABEL] #Stop current for|while|switch iteration or (only with LABEL)
#if_else|anonymous block
#Can target a specific for|while|switch iteration by specifying LABEL: before
#it (to avoid), e.g. LABEL: for ... or LABEL: if ...
continue [LABEL] #Same but only current loop, and only for|while
/=+===============================+=\
/ : : \
)==: TYPES :==(
\ :_______________________________: /
\=+===============================+=/
TYPING SYSTEM ==> # - weak: no type specified at Declaration
# - generic: native operators accepts any type, since each native type
# transtype to any (except OBJ->undefined|null)
# - dynamic: type is not checked at compile-time nor (since generic) run-time
AVAILABLE TYPES ==> # - simple: number|boolean|string|bigint|symbol|undefined|null
# - object (TYPE): Object and its children
# - native: Object|Array|Number|Boolean|String|Error|...
# - user-defined:
# - host objects: defined by browser (e.g. DOM elements)
typeof VAR #Returns "boolean|string|number|bigint|symbol|undefined|object|function"
#"object": includes null, excludes FUNC
Object.prototype.toString.call(VAL)->STR #Returns '[object NAME]' where NAME is (in priority order):
-|# - '[object OBJ[Symbol.toStringTag]]'
# - builtin:
# - 'Null|Undefined|Number|String|Boolean|BigInt|Symbol'
# - 'Object'
# - 'Array|[Shared]ArrayBuffer|DataView|[Big][U]Int|FloatNUMArray'
# - '[Async][Generator]Function'
# - 'Arguments'
# - 'RegExp|Date|Error|[Weak]Map|[Weak]Set|WeakRef|Realm'
# - 'Generator'
# - 'Promise'
# - 'Module'
# - 'Intl.*'
# - 'Math|JSON|Intl|Atomics|Reflect': the namespace itself
# - 'global'
# - not: Proxy
# - 'Object'
# (DOM only)
# - 'DOMError' (deprecated), 'DOMException'
/=+===============================+=\
/ : : \
)==: EQUALITY :==(
\ :_______________________________: /
\=+===============================+=/
VAL == VAL2
VAL != VAL2 #Implicit transtype
VAL === VAL2
VAL !== VAL2 #No implicit transtype
OBJ == OBJ2
OBJ != OBJ2
OBJ === OBJ2
OBJ !== OBJ2 #Same reference
Object.is(VAL, VAL2) -|#Same as ===, except !Object.is(+0,-0) and Object.is(NaN, NaN)
/=+===============================+=\
/ : : \
)==: TRANSTYPING :==(
\ :_______________________________: /
\=+===============================+=/
IMPLICIT TRANSTYPING ==> #Uses String|Boolean|Number|BigInt|Object(VAL)
EXPLICIT TRANSTYPING ==> #Prefer using String|Boolean|Number|BigInt|Object(VAL).
#Sometimes used (avoid):
# - BOOL: !!VAL
# - NUM: +VAL, VAL*1, VAL/1, ~~VAL, VAL|0, VAL-0
# - STR: VAL + ''
OBJ[Symbol.toPrimitive]('default') #Called when implicit type ambiguous, e.g. VAL + STR or VAL == VAL2
/=+===============================+=\
/ : : \
)==: UNDEFINED :==(
\ :_______________________________: /
\=+===============================+=/
undefined #Value of:
# - non-declared VAR: throw ReferenceError when used, except with typeof
# - declared but non-assigned VAR (including arguments and return value)
#Global variable, not keyword
# - non-configurable|writable
# - but can be shadowed by local VAR named "undefined"
typeof VAR === 'undefined' #Like VAR === undefined, except no ReferenceError if VAR undeclared
#Should never be necessary:
# - useless in local scopes
# - in global scope, use globalThis.VAR === undefined
/=+===============================+=\
/ : : \
)==: NULL :==(
\ :_______________________________: /
\=+===============================+=/
null #Special keyword indicating emptiness
VAL == null #Implicitly transtype to null|undefined, i.e. returns true for both
VAL === null|undefined #No implicit transtype
/=+===============================+=\
/ : : \
)==: BOOLEAN :==(
\ :_______________________________: /
\=+===============================+=/
true|false #BOOL
!BOOL
BOOL && BOOL2
BOOL || BOOL2
Boolean(VAL)->NUM #Used for explicit|implicit transtyping.
# - STR: '' false, '...' true
# - NUM|BIGINT: 1 true, 0 false
# - undefined|null: false
# - OBJ|SYM: true
/=+===============================+=\
/ : : \
)==: NUMBER :==(
\ :_______________________________: /
\=+===============================+=/
NUM #Always double-precision float (binary64)
#Can use TYPED_ARR for single-precision floats or 8|16|32-bits [u]ints
0xNUM
0XNUM #16 radix
0oNUM
0ONUM #8 radix
0bNUM
0BNUM #2 radix
NUM_... -|#Underscores can be added:
-|# - they are ignored and meant as separators
-|# - works with any radix except octals
NUM + - * / % NUM2 #
-NUM #
NUM++ ++NUM NUM-- --NUM #
NUM ** NUM2 #
NUM ~ & ^ | >> << >>> NUM2 #
NUM OP= NUM2 #E.g. NUM += NUM2
NUM < <= > >= NUM2 #
Number(VAL)->NUM #Used for explicit|implicit transtyping:
# - STR:
# - '': 0
# - 'NUM': NUM
# - trims whitespaces
# - others: NaN
# - BOOL: true 1, false 0
-|||# - BIGINT: TypeError
-|||# - can be explicitely converted though
-|||# - in which case, transtyped to [-]Infinity if out-of-bound
# - undefined: NaN
# - null: 0
-|# - SYM: TypeError
# - OBJ (in priority):
-|# - OBJ[Symbol.toPrimitive]('number')
# - OBJ.valueOf()
# - NaN
[Number.]parseFloat(VAL)->NUM #Like Number(VAL) but:
# - returns NaN for non-NUM|STR and ''
# - removes trailing non-numerical chars in STR
# - only understands decimal form
[Number.]parseInt(VAL[, NUM])->NUM #Same as [Number.]parseFloat() but:
# - removes decimals
# - understands decimal or hexadecimal form by default.
# - if NUM, forces radix
NUM.toFixed([NUM])->STR #Number of decimal digits.
#Might have exponential notation or not.
#Def|min NUM: 0. Max NUM: 100.
NUM.toExponential([NUM])->STR #Number of decimal digits.
#Always use exponential notation.
#Def|min NUM: 0. Max NUM: 100.
NUM.toPrecision([NUM])->STR #Number of integer+decimal digits, excluding leading decimals zeros if integer is 0
#Might have exponential notation or not.
#Min NUM: 1. Max NUM: 100.
#If no NUM, behaves like NUM.toString()
NUM.toString(RADIX)->STR #
Number.isInteger(NUM) -|#Does not coerce to NUM
[Number.]NaN #Returned e.g. by √-1, 0/0 or wrong NUM conversion
#Test:
# - NaN !== NaN but Object.is(NaN, NaN)
-|# - Number.isNaN(VAL): same as Object.is(VAL, NaN)
# - isNaN(VAL): same as Number.isNaN(Number(VAL))
[-]Infinity #Returned e.g. by overflow like 1e400, or 1/0
Number.POSITIVE_INFINITY|NEGATIVE_INFINITY #Test:
# - [-]Infinity === [-]Infinity
-|# - Number.isFinite(VAL): typeof VAL === 'number' && VAL !== [-]Infinity && !Number.isNaN(VAL)
# - isFinite(VAL): same as Number.isFinite(Number(VAL))
Number.MIN_VALUE #Closest to 0 (underflow) (about 5e-324)
Number.MAX_VALUE #After it is Infinity (overflow) (about 2e+308)
Number.MIN|MAX_SAFE_INTEGER -|#Smallest|highest integer that can be represented as a float precisely
-|#(about +|-1e16)
Number.isSafeInteger(NUM)->BOOL -|#Number.isInteger(NUM) && NUM >= Number.MIN_SAFE_INTEGER && NUM <= Number.MAX_SAFE_INTEGER
-|#Does not coerce to NUM
Number.EPSILON -|#NUM +|- NUM2 can create small discrepancies, e.g. 0.3 - 0.1 within a
-|#EPSILON range:
-|# - When comparing non-integer NUMs, should check NUM-NUM2 < +|-EPSILON
-|# - about 2e-16
/=+===============================+=\
/ : : \
)==: BIGINT :==(
\ :_______________________________: /
\=+===============================+=/
NUMn -|||#BIGINT. Infinite precision integer
-|||#Behaves like NUM:
-|||# - including octal, hex, binary notations
-|||# - including toString(RADIX)
-|||#Exceptions:
-|||# - integer not double:
-|||# - / % round towards 0
-|||# - cannot use >>> nor +NUMn
-|||# - throw on JSON.stringify()
-|||# - has its own typeof, constructor
-|||# - no BIGINT.toFixed|toPrecision|toExponential() (since it is integer)
BigInt(VAL)->NUM #Used for explicit|implicit transtyping.
# - STR|BOOL|OBJ|undefined: like NUM except SyntaxError instead of NaN
# - null|SYM: SyntaxError
# - NUM:
# - implicit: TypeError
# - exception: == === != !== < <= > >=
# - explicit: possible
# - transtyped to [-]Infinity if out-of-bound
BigInt.asUintN|asIntN(NUM, NUM2n)->NUM2n -|||#Enforce max size NUM bits on NUM2n
-|||#On overall, rotate to min|max value (according to NUM)
/=+===============================+=\
/ : : \
)==: STRING :==(
\ :_______________________________: /
\=+===============================+=/
"..." #Escapes everything but " newline and \ (including trailing)
'...' #Escapes everything but ' newline and \ (including trailing)
`...${EXPR}...` -|#"..." + EXPR + "..."
-|#Escapes everything (including " ' or newline) but ` ${ or \
\CHAR #Any backslash escape can be used except \a, \c et \e
NEWLINE ==> #OS-independent: '\n' is LF, '\r' is CR
#OS-dependent (CR+LF on Windows, LF others): terminal|file I/O
MAX LENGTH ==> #Standard: at most 2**53 - 1, i.e. ~9e15
#Engine-dependent:
# - v8: 2**29 - 24, i.e. ~5e8
# - SpiderMonkey: 2**30 - 2, i.e. ~1e9
# - SquirrelFish: 2**31 - 1, i.e. ~2e9
STR + STR2 #
STR += STR2 #
STR.concat(STR2...) #
STR < <= > >= #Char by char, code unit-wise
String(VAL)->STR #Used for explicit|implicit transtyping:
# - BOOL|NUM|undefined|null: 'BOOL|...'
# - BIGINT: 'NUM' (not 'NUMn')
-|# - SYM: 'Symbol(VAR)'
-|# - only with explicit String(SYM) or SYM.toString()
# - OBJ (in priority order):
-|# - OBJ[Symbol.toPrimitive]('string')
# - OBJ.toString()
# - FUNC|ARR|REGEXP|DATE|ERROR: see own doc
# - OBJ.valueOf()
# - Object.prototype.toString.call(VAL) (see its doc)
FUNC`...` -|#FUNC(STR_ARR, VAL...)->VAL:
FUNC `...` -|# - VAL... are each ${EXPR}
-|# - STR_ARR[.raw][NUM]:
-|# - each `...` in-between
-|# - including empty "" at beginning|end if starts|ends with ${EXPR}
-|# - if "raw", escape backslashes
-|# - STR_ARR.length === VAL.length + 1
-|# - special case for invalid backslash sequences (only if FUNC specified):
-|# - STR is undefined
-|# - escaped in STR_ARR.raw, e.g. '\\n'
-|#FUNC can be String.raw(), which concatenates all like normal template,
-|#except it escape backslashes
STR[NUM] #Read-only. undefined if out of range.
STR.charAt(NUM) #Same except "" if out of range
STR.at(NUM)->'CHAR' 16.6.0*-|~#Like STR[NUM] except -NUM is from end, and is not writable
STR.length #Number of characters
STR.match(REGEXP) #Like REGEXP.exec(STR), except that if g flag, returns all matches as ARR
#(or null)
STR.matchAll(REGEXP) -|#Returns ITERABLETOR that returns successive REGEXP.exec(STR)
-|#I.e. as opposed to STR.match(), when using a g flag, parenthesis groups and
-|#indices will be returned too
STR.search(REGEXP) #Like STR.indexOf() but with a REGEXP
STR.starts|endsWith|includes(STR2[, NUM]) -|#
STR.replace(REGEXP|STR2, STR3) #Returns STR, replacing REGEXP with STR3, which can contain:
# - $1, etc.: parenthesis group matches
# - $&: full match
# - $`: what's before full match
# - $': what's after full match
# - $$: $ literal
STR.replace(REGEXP|STR2,
FUNC($&, $1..., INDEX, STR)) #Returns STR, replacing REGEXP with FUNC(...)
STR.replaceAll(REGEXP|STR2, STR3)
STR.replaceAll(REGEXP|STR2, -|#Same as STR.replace(...) but STR2 implies a 'g' flag.
FUNC($&, $1..., INDEX, STR)) -|#If REGEXP, must have a 'g' flag.
STR.split(REGEXP|STR2[, UINT]) #Returns an ARR, with REGEXP|STR2 being split delimiter.
#If STR2 is '', means between each characters.
#If REGEXP contains parenthesis groups, each is included in ARR between each element.
#If UINT, does ARR.slice(0, UINT)
STR.repeat(NUM) -|#
OBJ[Symbol.match](...) -|#Methods to implement to be able to use STR.match(OBJ)
-|#or STR.startsWith|endsWith|includes(OBJ)
-|#Implemented by REGEXP
OBJ[Symbol.replace|split](...) -|#Methods to implement to be able to use STR.replace|split(OBJ).
-|#Implemented by REGEXP
OBJ[Symbol.search](...) -|#Methods to implement to be able to use STR.search(OBJ).
-|#Implemented by REGEXP
STR.toUpper|LowerCase() #
STR.trim() #
STR.trimLeft|Right() #Remove whitespaces (same as /\s/) on left and|or right.
STR.trimStart|End() |#Aliases for trimLeft|Right()
STR.padStart|End(NUM[, STR2]) -|#If STR.length < NUM, prepends|appends STR2 (def: ' ') until STR.length === NUM
STR.[lastI/i]ndexOf(STR[, NUM])
STR.slice([NUM[, NUM2]]) #Like ARR
STR.substring(NUM[, NUM2]) #Like .slice() except:
# - negative NUM2 -> 0
# - If NUM2 < NUM, swap
STR.substr(NUM[, NUM2]) #Like .slice() except:
# - NUM can be negative (index from end)
# - NUM2 is length, not index
en|decodeURI(STR) #Percent-encode any character not permitted in URIs, i.e. anything but:
# [:alnum:] - . _ ~ ! ' ( ) * # : ? & = + $ ; , / @
#Should be used for full URIs
#Uses UTF-8
#decodeURI() can throw URIError
en|decodeURIComponent(STR) #Same but also percent-encode characters that might have semantics in
#URIs parts:
# # : ? & = + $ ; , / @
#I.e. does not percent-encode the following (should escape if it has semantics
#for specific case):
# [:alnum:] - . _ ~ ! ' ( ) *
#Should be used for URI parts
[un]escape(STR) #Like en|decodeURIComponent() but using a different set of what's considered URI part:
# ~ ! ' ( ) # : ? & = $ ; ,
#I.e. does not percent-encode the following:
# [:alnum:] - . _ * + / @
#Also, uses UTF-16, with Unicode chars percent encoded as %uUUUU, not a series of %XX
#Deprecated
/=+===============================+=\
/ : : \
)==: UNICODE :==(
\ :_______________________________: /
\=+===============================+=/
ENCODING ==> #UTF-16:
# - S_CODEPOINT: 1 character === 1 codepoint
# - CODEPOINT: 1 character === 1 codepoint (<U+10000) or 2 surrogate codepoints (>=U+10000)
# - isolated|inverted surrogate pairs are not invalid: they are considered their own character|codepoint instead
#Exceptions:
# - encode|decodeURI[Component]() uses UTF-8
# - the platform (Node.js, Web APIs) provides with encoding-specific operations. often with UTF-8
S_CODEPOINT #Single Unicode character STR. Any, even U+10FFFF
CODEPOINT #Like S_CODEPOINT except > U+FFFF treats each surrogate as own character.
#All STR operations use CODEPOINTs:
# - including STR.length, STR[NUM], STR.*(), comparison, max length
# - except:
# - STR iteration
# - STR.to[Locale]Lower|UpperCase(), STR.trim*()
# - \u{}, String.fromCodePoint(), STR.codePointAt(), /REGEXP/u
[S_]CODEPOINT[_NUM] #Same as NUM
\uCODEPOINT_HEXA #CODEPOINT in a STR
\u{S_CODEPOINT_HEXA} -|#S_CODEPOINT in a STR
String.fromCharCode(CODEPOINT_NUM...)->STR #
String.fromCodePoint(S_CODEPOINT_NUM...)->STR -|#Returns STR
STR.charCodeAt(NUM)->CODEPOINT #NUM is CODEPOINT-wise
#For > U+FFFF, if NUM is on:
# - the first|second surrogate pair: CODEPOINT is returned
#If NUM out-of-range, returns NaN.
STR.codePointAt(NUM)->S_CODEPOINT -|#NUM is CODEPOINT-wise
-|#For > U+FFFF, if NUM is on:
-|# - the first surrogate pair: S_CODEPOINT is returned
-|# - the second surrogate pair: CODEPOINT is returned
-|#If NUM out-of-range, returns undefined.
/REGEXP/u -|# - operate with S_CODEPOINT instead of CODEPOINT
-|# - for example for . [] {NUM,NUM2} etc.
-|# - stricter REGEXP syntax enforcement, e.g. /{/ throws
-|# - allow using \p or \P
STR.normalize([STR2]) -#Some codepoint sequences are equivalent, e.g. with diacretics
-#Equivalence types:
-# - canonical: same abstract character, including visual appearance and behavior
-# - example: '\u00e9' (é) (composed) and '\u0065\u0301' (e ́) (decomposed)
-# - compatibility: looser superset, i.e. enough if can be treated alike
-# - examples:
-# - '\ufb00' (ff ) (composed) and '\u0066' (ff) (decomposed)
-# - '\u24b9' (Ⓓ ) (composed) and '\u0044' (D) (decomposed)
-#Can be:
-# - "NFC" (def): decomposes then compose (canonical)
-# - "NFD": decompose (canonical)
-# - "NFKC": decompose then compose (compatibility)
-# - "NFKD": decompose (compatibility)
STR.isWellFormed()->BOOL 20.0.0*-|#False if contains isolated|inverted surrogate pairs
STR.toWellFormed()->STR 20.0.0*-|#Replaces isolated|inverted surrogate pairs by U+FFFD
/=+===============================+=\
/ : : \
)==: SYMBOLS :==(
\ :_______________________________: /
\=+===============================+=/
Symbol([STR]) -|#SYM
SYM.description -|#STR
SYM == != === !== SYM -|#Symbols are compared by identify, regardless of SYM.description
SYM.toString()->'Symbol(STR)' -|#STR is SYM.description
OBJ[SYM] -|#Same as OBJ["RANDOM"], semantically for private members.
-|#Different methods to enumerate (see above)
-|#SYM properties ignored by JSON.stringify()
Symbol.for(STR) -|#Like Symbol(STR), except "register" it to a global store using STR as a key,
-|#so that Symbol.for(STR) === Symbol.for(STR)
Symbol.keyFor(SYM) -|#Returns STR if SYM was created as Symbol.for(STR), undefined otherwise.
WELL-KNOWN SYMBOLS ==> -|#SYM that can be used to override native behavior.
-|#E.g. Symbol.iterator
-|#When printed, sometimes abbreviated to @@VAR
/=+===============================+=\
/ : : \
)==: OBJECTS :==(
\ :_______________________________: /
\=+===============================+=/
[new] Object(VAL) #Used for implicit|explicit conversion.
#For any type:
# - new type is OBJ, i.e. different type
# - but behavior is same thanks to implicit transtyping
#For Number|BigInt|String|Boolean:
# - can also use new TYPE(VAL)
#For undefined|null:
# - prototype is null
# - no implicit transtyping
#All OBJs inherit from Object except Object.create(null)
OBJ.VAR #Access property (can be any type)
OBJ['VAR'] #OBJ.VAR has same naming restrictions as QUAL VAR, except can be a reserved word
#OBJ['VAR'] can use any valid STR
#Throws with undefined|null
OBJ?.VAR #Like OBJ == null ? undefined : OBJ.VAR
OBJ?.['VAR'] #Like OBJ == null ? undefined : OBJ['VAR']
{ VAR[: VAL] ... } #Literal OBJ.
#If could be interpreted as a { ... } structure (e.g. beginning of line),
#wrap with ()
#VAR can either:
# - be "VAR" or 'VAR': any valid STR
# - be unquoted, with same naming restrictions as QUAL VAR except:
# - can be reserved keywords
# - can be any NUM, which will be converted to STR
-|#Def VAL is VAR
-|#VAR can be [STR], for dynamic property name
-|#If duplicate key, the last one will overwrite the ones before.
{ FUNC() {...} ... } -|#Same as { FUNC: function FUNC() {...} ... }
PROPERTIES ORDER ==> #Guaranteed to be in that order:
# - 'NUM', sorted numerically
# - STR, sorted by creation time
# - SYM, sorted by creation time
OWN / ENUMERABLE ==> # +-------------------------------------------------------+-------------------------------+
# | Own | Own+inherited |
# +------------+-------------------------------------------------------+-------------------------------+
# | enum | OBJ.propertyIsEnumerable('VAR'|SYM)->BOOL | for (QUAL NOT_SYM_VAR in OBJ) |
# | | Object.keys(OBJ)->'VAR'_ARR | |
# | | Object.values|entries|fromEntries(...) | |
# | | Object.assign(...), { ...OBJ } | |
# +------------+-------------------------------------------------------+-------------------------------+
# | [non-]enum | OBJ.hasOwnProperty('VAR'|SYM)->BOOL | 'VAR'|SYM|#PROP in OBJ |
# | | Object.hasOwn(OBJ, 'VAR'|SYM)->BOOL | |
# | | Reflect.ownKeys(OBJ)=>'VAR'|SYM_ARR | |
# | | Object.getOwnPropertyNames(OBJ)->'VAR'_ARR | |
# | | Object.getOwnPropertySymbols(OBJ)->SYM_ARR | |
# | | Object.getOwnPropertyDescriptor(OBJ, 'VAR'|SYM)->OBJ2 | |
# | | Object.getOwnPropertyDescriptors(OBJ)->OBJ3 | |
# +------------+-------------------------------------------------------+-------------------------------+
'VAR'|SYM in OBJ #Returns true if OBJ['VAR'|SYM] is member
#Negation: !('VAR' in OBJ)
#PROP in OBJ 16.5.0*-|#Same for private #PROP
OBJ.hasOwnProperty('VAR'|SYM)->BOOL #Returns true if OBJ['VAR'|SYM] is own
Object.hasOwn(OBJ, 'VAR'|SYM)->BOOL 16.9.0*-|#Same
OBJ.propertyIsEnumerable('VAR'|SYM)->BOOL #Returns true if OBJ['VAR'|SYM] is own + enumerable
Object.keys(OBJ)->'VAR'_ARR #Returns keys that are own + enumerable + not SYMs
Reflect.ownKeys(OBJ)->'VAR'|SYM_ARR #Returns keys that are own
Object.getOwnPropertyNames(OBJ)->'VAR'_ARR #Returns keys that are own + not SYMs
Object.getOwnPropertySymbols(OBJ)->SYM_ARR #Returns keys that are own + SYMs
Object.values(OBJ) -|#Same as Object.keys() but for values
Object.entries(OBJ) -|#Same as Object.keys() but for [KEY, VALUE]
Object.fromEntries(ITERABLE) -|#Inverse Object.entries(), i.e. from ITERABLE of [KEY, VALUE] to OBJ
-|#As opposed to Object.entries(), KEY that SYM are not skipped
Object.assign(OBJ[, OBJ2...]) -|#Shallow copy of own enumerable OBJ2 members (including SYMs) to OBJ, which is returned.
-|#Properties copied in OBJ are:
-|# - always configurable|writable, even if OBJ2 members were not
-|# - resolved, if OBJ2 members were getters
{ [...] ...OBJ2 [...] } -|#Same as Object.assign({}, OBJ2, ...)
[QUAL] { [...] ...OBJ } = OBJ2 -|#Does Object.assign(OBJ, OBJ2), except the parts mentioned in ...
/=+===============================+=\
/ : : \
)==: OBJECT DESCRIPTORS :==(
\ :_______________________________: /
\=+===============================+=/
{ get|set VAR(...) {...} } #Like { VAR(...) {...} } followed by Object.defineProperty() with configurable|enumerable true
Object.defineProperty(OBJ, 'VAR'|SYM, OBJ2) #Assign OBJ['VAR'|SYM] = VAL, where VAL depends on OBJ2 ('descriptors'):
# - either (def: value undefined):
# - value VAL
# - get and|or set:
# - get()->VAL
# - called at OBJ.VAR
# - def: returns undefined
# - set(VAL)
# - called at OBJ.VAR = VAL
# - `this` is OBJ
# - no return value, i.e. must be modified
# - must not set this.VAR to avoid infinite recursion
# - def: TypeError on set
# - enumerable BOOL (def: false):
# - if false, not listed by Object.keys|...(), OBJ.propertyIsEnumerable() and for (QUAL STR in OBJ)
# - writable BOOL (def: false):
# - if false, throws TypeError if OBJ.VAR = VAL
# - even if VAL did not change
# - even if VAR is inherited through the __proto__ chain
# - but can still Object.defineProperty() if configurable
# - not possible with get|set():
# - always undefined
# - setting it throws
# - configurable BOOL (def: false):
# - if false, throws TypeError:
# - if:
# - delete OBJ.VAR
# - set configurable|writable false -> true
# - set enumerable|get|set -> !== value
# - go from get|set <-> value
# - not if:
# - set value, or OBJ.VAR = VAL
# - except if current writable false
# - set writable true -> false
# - VAR is inherited through the __proto__ chain
#If own property already exists, default values are current descriptors instead.
Object.getOwnPropertyDescriptor(OBJ, 'VAR'|SYM) #Returns OBJ.VAR descriptor OBJ2
->OBJ2 #Even if not declared through Object.defineProperty()
#Returns undefined if does not exists or is not own.
#Including SYMs
Object.defineProperties(OBJ, OBJ3)
Object.getOwnPropertyDescriptors(OBJ)->OBJ3 #Same but using OBJ3 { 'VAR': OBJ2 ... } instead.
Object.preventExtensions(OBJ) #Make OBJ non-extensible, i.e. TypeError if:
# - adding new property
# - setting __proto__
#Not recursive.
Object.isExtensible(OBJ) #
Object.seal(OBJ) #Make OBJ non-extensible, non-configurable
#Not recursive.
Object.isSealed(OBJ) #
Object.freeze(OBJ) #Make OBJ non-extensible, non-configurable, non-writable (except get|set())
#Not recursive.
Object.isFrozen(OBJ) #
/=+===============================+=\
/ : : \
)==: PROTOTYPES :==(
\ :_______________________________: /
\=+===============================+=/
OBJ.__proto__ #When OBJ.VAR is not defined, OBJ.__proto__.VAR is tried
# - recursively (prototype chain)
# - the last __proto__ is null
#Setting OBJ.__proto__[...].VAR creates OBJ.VAR instead
# - including with Object.defineProperty() and delete
# - even if value did not change
#I.e. inheritance is prototype-based.
#__proto__ itself is considered an inherited, non-enumerable, writable, configurable property
Object.getPrototypeOf(OBJ)->VAL #Same but less standard and:
# - returns `null` instead of `undefined` for null prototype
# - does not return `undefined` if no prototype in the chain is Object.prototype
Object.setPrototypeOf(OBJ, VAL)->OBJ -|#Same as OBJ.__proto__ = VAL (to avoid because performance issues)
OBJ.isPrototypeOf(OBJ2) #Returns true if OBJ2.__proto__[...] === OBJ
#I.e. if isPrototypeOf TYPE, also true for TYPE_PARENT
#Always false for non-OBJs, but does not throw.