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core-js

Standard library

core-js

Modular standard library for JavaScript. Includes polyfills for ECMAScript 5, ECMAScript 6: promises, symbols, collections, iterators, typed arrays, ECMAScript 7+ proposals, setImmediate, etc. Some additional features such as dictionaries or extended partial application. You can require only needed features or use it without global namespace pollution.

Example:

Array.from(new Set([1, 2, 3, 2, 1]));          // => [1, 2, 3] 
'*'.repeat(10);                                // => '**********' 
Promise.resolve(32).then(x => console.log(x)); // => 32 
setImmediate(x => console.log(x), 42);         // => 42 

Without global namespace pollution:

var core = require('core-js/library'); // With a modular system, otherwise use global `core` 
core.Array.from(new core.Set([1, 2, 3, 2, 1]));     // => [1, 2, 3] 
core.String.repeat('*', 10);                        // => '**********' 
core.Promise.resolve(32).then(x => console.log(x)); // => 32 
core.setImmediate(x => console.log(x), 42);         // => 42 
npm i core-js
bower install core.js
// Default 
require('core-js');
// Without global namespace pollution 
var core = require('core-js/library');
// Shim only 
require('core-js/shim');

If you need complete build for browser, use builds from core-js/client path:

Warning: if you use core-js with the extension of native objects, require all needed core-js modules at the beginning of entry point of your application, otherwise, conflicts may occur.

You can require only needed modules.

require('core-js/fn/set');
require('core-js/fn/array/from');
require('core-js/fn/array/find-index');
Array.from(new Set([1, 2, 3, 2, 1])); // => [1, 2, 3] 
[1, 2, NaN, 3, 4].findIndex(isNaN);   // => 2 
 
// or, w/o global namespace pollution: 
 
var Set       = require('core-js/library/fn/set');
var from      = require('core-js/library/fn/array/from');
var findIndex = require('core-js/library/fn/array/find-index');
from(new Set([1, 2, 3, 2, 1]));      // => [1, 2, 3] 
findIndex([1, 2, NaN, 3, 4], isNaN); // => 2 

Available entry points for methods / constructors, as above examples, and namespaces: for example, core-js/es6/array (core-js/library/es6/array) contains all ES6 Array features, core-js/es6 (core-js/library/es6) contains all ES6 features.

  • modules path is internal API, does not inject all required dependencies and can be changed in minor or patch releases. Use it only for a custom build and / or if you know what are you doing.
  • core-js is extremely modular and uses a lot of very tiny modules, because of that for usage in browsers bundle up core-js instead of usage loader for each file, otherwise, you will have hundreds of requests.

In the library version, we can't pollute prototypes of native constructors. Because of that, prototype methods transformed to static methods like in examples above. babel runtime transformer also can't transform them. But with transpilers we can use one more trick - bind operator and virtual methods. Special for that, available /virtual/ entry points. Example:

import fill from 'core-js/library/fn/array/virtual/fill';
import findIndex from 'core-js/library/fn/array/virtual/find-index';
 
Array(10)::fill(0).map((a, b) => b * b)::findIndex(it => it && !(it % 8)); // => 4 
 
// or 
 
import {fill, findIndex} from 'core-js/library/fn/array/virtual';
 
Array(10)::fill(0).map((a, b) => b * b)::findIndex(it => it && !(it % 8)); // => 4 
 
npm i core-js && cd node_modules/core-js && npm i
npm run grunt build:core.dict,es6 -- --blacklist=es6.promise,es6.math --library=on --path=custom uglify

Where core.dict and es6 are modules (namespaces) names, which will be added to the build, es6.promise and es6.math are modules (namespaces) names, which will be excluded from the build, --library=on is flag for build without global namespace pollution and custom is target file name.

Available namespaces: for example, es6.array contains ES6 Array features, es6 contains all modules whose names start with es6.

core-js-builder package exports a function that takes the same parameters as the build target from the previous section. This will conditionally include or exclude certain parts of core-js:

require('core-js-builder')({
  modules: ['es6', 'core.dict'], // modules / namespaces 
  blacklist: ['es6.reflect'],    // blacklist of modules / namespaces, by default - empty list 
  library: false,                // flag for build without global namespace pollution, by default - false 
  umd: true                      // use UMD wrapper for export `core` object, by default - true 
}).then(code => {
  // ... 
}).catch(error => {
  // ... 
});

Tested in:

  • Chrome 26+
  • Firefox 4+
  • Safari 5+
  • Opera 12+
  • Internet Explorer 6+ (sure, IE8- with ES3 limitations)
  • Edge
  • Android Browser 2.3+
  • iOS Safari 5.1+
  • PhantomJS 1.9 / 2.1
  • NodeJS 0.8+

...and it doesn't mean core-js will not work in other engines, they just have not been tested.

CommonJS entry points:

core-js(/library)       <- all features
core-js(/library)/shim  <- only polyfills

All features moved to the es6 namespace, here just a list of features:

Object
  .create(proto | null, descriptors?)    -> object
  .getPrototypeOf(object)                -> proto | null
  .defineProperty(target, key, desc)     -> target, cap for ie8-
  .defineProperties(target, descriptors) -> target, cap for ie8-
  .getOwnPropertyDescriptor(object, key) -> desc
  .getOwnPropertyNames(object)           -> array
  .keys(object)                          -> array
  .seal(object)                          -> object, cap for ie8-
  .freeze(object)                        -> object, cap for ie8-
  .preventExtensions(object)             -> object, cap for ie8-
  .isSealed(object)                      -> bool, cap for ie8-
  .isFrozen(object)                      -> bool, cap for ie8-
  .isExtensible(object)                  -> bool, cap for ie8-
Array
  .isArray(var)                                -> bool
  #slice(start?, end?)                         -> array, fix for ie7-
  #join(string = ',')                          -> string, fix for ie7-
  #indexOf(var, from?)                         -> int
  #lastIndexOf(var, from?)                     -> int
  #every(fn(val, index, @), that)              -> bool
  #some(fn(val, index, @), that)               -> bool
  #forEach(fn(val, index, @), that)            -> void
  #map(fn(val, index, @), that)                -> array
  #filter(fn(val, index, @), that)             -> array
  #reduce(fn(memo, val, index, @), memo?)      -> var
  #reduceRight(fn(memo, val, index, @), memo?) -> var
  #sort(fn?)                                   -> @, fixes for some engines
Function
  #bind(object, ...args) -> boundFn(...args)
String
  #split(separator, limit) -> array
  #trim()                  -> str
RegExp
  #toString() -> str
Number
  #toFixed(digits)        -> string
  #toPrecision(precision) -> string
parseInt(str, radix) -> int
parseFloat(str)      -> num
Date
  .now()         -> int
  #toISOString() -> string
  #toJSON()      -> string

CommonJS entry points:

core-js(/library)/es5

CommonJS entry points:

core-js(/library)/es6

Modules es6.object.assign, es6.object.is, es6.object.set-prototype-of and es6.object.to-string.

In ES6 most Object static methods should work with primitives. Modules es6.object.freeze, es6.object.seal, es6.object.prevent-extensions, es6.object.is-frozen, es6.object.is-sealed, es6.object.is-extensible, es6.object.get-own-property-descriptor, es6.object.get-prototype-of, es6.object.keys and es6.object.get-own-property-names.

Just ES5 features: es6.object.create, es6.object.define-property and es6.object.define-properties.

Object
  .assign(target, ...src)                -> target
  .is(a, b)                              -> bool
  .setPrototypeOf(target, proto | null)  -> target (required __proto__ - IE11+)
  .create(object | null, descriptors?)   -> object
  .getPrototypeOf(var)                   -> object | null
  .defineProperty(object, key, desc)     -> target
  .defineProperties(object, descriptors) -> target
  .getOwnPropertyDescriptor(var, key)    -> desc | undefined
  .keys(var)                             -> array
  .getOwnPropertyNames(var)              -> array
  .freeze(var)                           -> var
  .seal(var)                             -> var
  .preventExtensions(var)                -> var
  .isFrozen(var)                         -> bool
  .isSealed(var)                         -> bool
  .isExtensible(var)                     -> bool
  #toString()                            -> string, ES6 fix: @@toStringTag support

CommonJS entry points:

core-js(/library)/es6/object
core-js(/library)/fn/object/assign
core-js(/library)/fn/object/is
core-js(/library)/fn/object/set-prototype-of
core-js(/library)/fn/object/get-prototype-of
core-js(/library)/fn/object/create
core-js(/library)/fn/object/define-property
core-js(/library)/fn/object/define-properties
core-js(/library)/fn/object/get-own-property-descriptor
core-js(/library)/fn/object/keys
core-js(/library)/fn/object/get-own-property-names
core-js(/library)/fn/object/freeze
core-js(/library)/fn/object/seal
core-js(/library)/fn/object/prevent-extensions
core-js(/library)/fn/object/is-frozen
core-js(/library)/fn/object/is-sealed
core-js(/library)/fn/object/is-extensible
core-js/fn/object/to-string

Examples:

var foo = {q: 1, w: 2}
  , bar = {e: 3, r: 4}
  , baz = {t: 5, y: 6};
Object.assign(foo, bar, baz); // => foo = {q: 1, w: 2, e: 3, r: 4, t: 5, y: 6} 
 
Object.is(NaN, NaN); // => true 
Object.is(0, -0);    // => false 
Object.is(42, 42);   // => true 
Object.is(42, '42'); // => false 
 
function Parent(){}
function Child(){}
Object.setPrototypeOf(Child.prototype, Parent.prototype);
new Child instanceof Child;  // => true 
new Child instanceof Parent; // => true 
 
var O = {};
O[Symbol.toStringTag] = 'Foo';
'' + O; // => '[object Foo]' 
 
Object.keys('qwe'); // => ['0', '1', '2'] 
Object.getPrototypeOf('qwe') === String.prototype; // => true 

Modules es6.function.name, es6.function.has-instance. Just ES5: es6.function.bind.

Function
  #bind(object, ...args) -> boundFn(...args)
  #name                  -> string (IE9+)
  #@@hasInstance(var)    -> bool

CommonJS entry points:

core-js/es6/function
core-js/fn/function/name
core-js/fn/function/has-instance
core-js/fn/function/bind
core-js/fn/function/virtual/bind

Example:

(function foo(){}).name // => 'foo' 
 
console.log.bind(console, 42)(43); // => 42 43 

Modules es6.array.from, es6.array.of, es6.array.copy-within, es6.array.fill, es6.array.find, es6.array.find-index, es6.array.iterator. ES5 features with fixes: es6.array.is-array, es6.array.slice, es6.array.join, es6.array.index-of, es6.array.last-index-of, es6.array.every, es6.array.some, es6.array.for-each, es6.array.map, es6.array.filter, es6.array.reduce, es6.array.reduce-right, es6.array.sort.

Array
  .from(iterable | array-like, mapFn(val, index)?, that) -> array
  .of(...args)                                           -> array
  .isArray(var)                                          -> bool
  #copyWithin(target = 0, start = 0, end = @length)      -> @
  #fill(val, start = 0, end = @length)                   -> @
  #find(fn(val, index, @), that)                         -> val
  #findIndex(fn(val, index, @), that)                    -> index | -1
  #values()                                              -> iterator
  #keys()                                                -> iterator
  #entries()                                             -> iterator
  #join(string = ',')                                    -> string, fix for ie7-
  #slice(start?, end?)                                   -> array, fix for ie7-
  #indexOf(var, from?)                                   -> index | -1
  #lastIndexOf(var, from?)                               -> index | -1
  #every(fn(val, index, @), that)                        -> bool
  #some(fn(val, index, @), that)                         -> bool
  #forEach(fn(val, index, @), that)                      -> void
  #map(fn(val, index, @), that)                          -> array
  #filter(fn(val, index, @), that)                       -> array
  #reduce(fn(memo, val, index, @), memo?)                -> var
  #reduceRight(fn(memo, val, index, @), memo?)           -> var
  #sort(fn?)                                             -> @, invalid arguments fix
  #@@iterator()                                          -> iterator (values)
  #@@unscopables                                         -> object (cap)
Arguments
  #@@iterator() -> iterator (values, available only in core-js methods)

CommonJS entry points:

core-js(/library)/es6/array
core-js(/library)/fn/array/from
core-js(/library)/fn/array/of
core-js(/library)/fn/array/is-array
core-js(/library)/fn/array/iterator
core-js(/library)/fn/array/copy-within
core-js(/library)/fn/array/fill
core-js(/library)/fn/array/find
core-js(/library)/fn/array/find-index
core-js(/library)/fn/array/values
core-js(/library)/fn/array/keys
core-js(/library)/fn/array/entries
core-js(/library)/fn/array/slice
core-js(/library)/fn/array/join
core-js(/library)/fn/array/index-of
core-js(/library)/fn/array/last-index-of
core-js(/library)/fn/array/every
core-js(/library)/fn/array/some
core-js(/library)/fn/array/for-each
core-js(/library)/fn/array/map
core-js(/library)/fn/array/filter
core-js(/library)/fn/array/reduce
core-js(/library)/fn/array/reduce-right
core-js(/library)/fn/array/sort
core-js(/library)/fn/array/virtual/iterator
core-js(/library)/fn/array/virtual/copy-within
core-js(/library)/fn/array/virtual/fill
core-js(/library)/fn/array/virtual/find
core-js(/library)/fn/array/virtual/find-index
core-js(/library)/fn/array/virtual/values
core-js(/library)/fn/array/virtual/keys
core-js(/library)/fn/array/virtual/entries
core-js(/library)/fn/array/virtual/slice
core-js(/library)/fn/array/virtual/join
core-js(/library)/fn/array/virtual/index-of
core-js(/library)/fn/array/virtual/last-index-of
core-js(/library)/fn/array/virtual/every
core-js(/library)/fn/array/virtual/some
core-js(/library)/fn/array/virtual/for-each
core-js(/library)/fn/array/virtual/map
core-js(/library)/fn/array/virtual/filter
core-js(/library)/fn/array/virtual/reduce
core-js(/library)/fn/array/virtual/reduce-right
core-js(/library)/fn/array/virtual/sort

Examples:

Array.from(new Set([1, 2, 3, 2, 1]));      // => [1, 2, 3] 
Array.from({0: 1, 1: 2, 2: 3, length: 3}); // => [1, 2, 3] 
Array.from('123', Number);                 // => [1, 2, 3] 
Array.from('123', function(it){
  return it * it;
});                                        // => [1, 4, 9] 
 
Array.of(1);       // => [1] 
Array.of(1, 2, 3); // => [1, 2, 3] 
 
var array = ['a', 'b', 'c'];
 
for(var val of array)console.log(val);          // => 'a', 'b', 'c' 
for(var val of array.values())console.log(val); // => 'a', 'b', 'c' 
for(var key of array.keys())console.log(key);   // => 0, 1, 2 
for(var [key, val] of array.entries()){
  console.log(key);                             // => 0, 1, 2 
  console.log(val);                             // => 'a', 'b', 'c' 
}
 
function isOdd(val){
  return val % 2;
}
[4, 8, 15, 16, 23, 42].find(isOdd);      // => 15 
[4, 8, 15, 16, 23, 42].findIndex(isOdd); // => 2 
[4, 8, 15, 16, 23, 42].find(isNaN);      // => undefined 
[4, 8, 15, 16, 23, 42].findIndex(isNaN); // => -1 
 
Array(5).fill(42); // => [42, 42, 42, 42, 42] 
 
[1, 2, 3, 4, 5].copyWithin(0, 3); // => [4, 5, 3, 4, 5] 

Modules es6.string.from-code-point, es6.string.raw, es6.string.iterator, es6.string.code-point-at, es6.string.ends-with, es6.string.includes, es6.string.repeat, es6.string.starts-with and es6.string.trim.

Annex B HTML methods. Ugly, but it's also the part of the spec. Modules es6.string.anchor, es6.string.big, es6.string.blink, es6.string.bold, es6.string.fixed, es6.string.fontcolor, es6.string.fontsize, es6.string.italics, es6.string.link, es6.string.small, es6.string.strike, es6.string.sub and es6.string.sup.

String
  .fromCodePoint(...codePoints) -> str
  .raw({raw}, ...substitutions) -> str
  #includes(str, from?) -> bool
  #startsWith(str, from?) -> bool
  #endsWith(str, from?) -> bool
  #repeat(num) -> str
  #codePointAt(pos) -> uint
  #trim() -> str, ES6 fix
  #anchor(name)     -> str
  #big()            -> str
  #blink()          -> str
  #bold()           -> str
  #fixed()          -> str
  #fontcolor(color) -> str
  #fontsize(size)   -> str
  #italics()        -> str
  #link(url)        -> str
  #small()          -> str
  #strike()         -> str
  #sub()            -> str
  #sup()            -> str
  #@@iterator() -> iterator (code points)

CommonJS entry points:

core-js(/library)/es6/string
core-js(/library)/fn/string/from-code-point
core-js(/library)/fn/string/raw
core-js(/library)/fn/string/includes
core-js(/library)/fn/string/starts-with
core-js(/library)/fn/string/ends-with
core-js(/library)/fn/string/repeat
core-js(/library)/fn/string/code-point-at
core-js(/library)/fn/string/trim
core-js(/library)/fn/string/anchor
core-js(/library)/fn/string/big
core-js(/library)/fn/string/blink
core-js(/library)/fn/string/bold
core-js(/library)/fn/string/fixed
core-js(/library)/fn/string/fontcolor
core-js(/library)/fn/string/fontsize
core-js(/library)/fn/string/italics
core-js(/library)/fn/string/link
core-js(/library)/fn/string/small
core-js(/library)/fn/string/strike
core-js(/library)/fn/string/sub
core-js(/library)/fn/string/sup
core-js(/library)/fn/string/iterator
core-js(/library)/fn/string/virtual/includes
core-js(/library)/fn/string/virtual/starts-with
core-js(/library)/fn/string/virtual/ends-with
core-js(/library)/fn/string/virtual/repeat
core-js(/library)/fn/string/virtual/code-point-at
core-js(/library)/fn/string/virtual/trim
core-js(/library)/fn/string/virtual/anchor
core-js(/library)/fn/string/virtual/big
core-js(/library)/fn/string/virtual/blink
core-js(/library)/fn/string/virtual/bold
core-js(/library)/fn/string/virtual/fixed
core-js(/library)/fn/string/virtual/fontcolor
core-js(/library)/fn/string/virtual/fontsize
core-js(/library)/fn/string/virtual/italics
core-js(/library)/fn/string/virtual/link
core-js(/library)/fn/string/virtual/small
core-js(/library)/fn/string/virtual/strike
core-js(/library)/fn/string/virtual/sub
core-js(/library)/fn/string/virtual/sup
core-js(/library)/fn/string/virtual/iterator

Examples:

for(var val of 'a𠮷b'){
  console.log(val); // => 'a', '𠮷', 'b' 
}
 
'foobarbaz'.includes('bar');      // => true 
'foobarbaz'.includes('bar', 4);   // => false 
'foobarbaz'.startsWith('foo');    // => true 
'foobarbaz'.startsWith('bar', 3); // => true 
'foobarbaz'.endsWith('baz');      // => true 
'foobarbaz'.endsWith('bar', 6);   // => true 
 
'string'.repeat(3); // => 'stringstringstring' 
 
'𠮷'.codePointAt(0); // => 134071 
String.fromCodePoint(97, 134071, 98); // => 'a𠮷b' 
 
var name = 'Bob';
String.raw`Hi\n${name}!`;           // => 'Hi\\nBob!' (ES6 template string syntax) 
String.raw({raw: 'test'}, 0, 1, 2); // => 't0e1s2t' 
 
'foo'.bold();                     // => '<b>foo</b>' 
'bar'.anchor('a"b');              // => '<a name="a&quot;b">bar</a>' 
'baz'.link('http://example.com'); // => '<a href="http://example.com">baz</a>' 

Modules es6.regexp.constructor and es6.regexp.flags.

Support well-known symbols @@match, @@replace, @@search and @@split, modules es6.regexp.match, es6.regexp.replace, es6.regexp.search and es6.regexp.split.

[new] RegExp(pattern, flags?) -> regexp, ES6 fix: can alter flags (IE9+)
  #flags -> str (IE9+)
  #toString() -> str, ES6 fixes
  #@@match(str)             -> array | null
  #@@replace(str, replacer) -> string
  #@@search(str)            -> index
  #@@split(str, limit)      -> array
String
  #match(tpl)             -> var, ES6 fix for support @@match
  #replace(tpl, replacer) -> var, ES6 fix for support @@replace
  #search(tpl)            -> var, ES6 fix for support @@search
  #split(tpl, limit)      -> var, ES6 fix for support @@split, some fixes for old engines

CommonJS entry points:

core-js/es6/regexp
core-js/fn/regexp/constructor
core-js(/library)/fn/regexp/flags
core-js/fn/regexp/to-string
core-js/fn/regexp/match
core-js/fn/regexp/replace
core-js/fn/regexp/search
core-js/fn/regexp/split

Examples:

RegExp(/./g, 'm'); // => /./m 
 
/foo/.flags;    // => '' 
/foo/gim.flags; // => 'gim' 
 
'foo'.match({[Symbol.match]: _ => 1});     // => 1 
'foo'.replace({[Symbol.replace]: _ => 2}); // => 2 
'foo'.search({[Symbol.search]: _ => 3});   // => 3 
'foo'.split({[Symbol.split]: _ => 4});     // => 4 
 
RegExp.prototype.toString.call({source: 'foo', flags: 'bar'}); // => '/foo/bar' 

Module es6.number.constructor. Number constructor support binary and octal literals, example:

Number('0b1010101'); // => 85 
Number('0o7654321'); // => 2054353 

Modules es6.number.epsilon, es6.number.is-finite, es6.number.is-integer, es6.number.is-nan, es6.number.is-safe-integer, es6.number.max-safe-integer, es6.number.min-safe-integer, es6.number.parse-float, es6.number.parse-int, es6.number.to-fixed, es6.number.to-precision, es6.parse-int, es6.parse-float.

[new] Number(var)         -> number | number object
  .isFinite(num)          -> bool
  .isNaN(num)             -> bool
  .isInteger(num)         -> bool
  .isSafeInteger(num)     -> bool
  .parseFloat(str)        -> num
  .parseInt(str)          -> int
  .EPSILON                -> num
  .MAX_SAFE_INTEGER       -> int
  .MIN_SAFE_INTEGER       -> int
  #toFixed(digits)        -> string, fixes
  #toPrecision(precision) -> string, fixes
parseFloat(str)           -> num, fixes
parseInt(str)             -> int, fixes

CommonJS entry points:

core-js(/library)/es6/number
core-js/es6/number/constructor
core-js(/library)/fn/number/is-finite
core-js(/library)/fn/number/is-nan
core-js(/library)/fn/number/is-integer
core-js(/library)/fn/number/is-safe-integer
core-js(/library)/fn/number/parse-float
core-js(/library)/fn/number/parse-int
core-js(/library)/fn/number/epsilon
core-js(/library)/fn/number/max-safe-integer
core-js(/library)/fn/number/min-safe-integer
core-js(/library)/fn/number/to-fixed
core-js(/library)/fn/number/to-precision
core-js(/library)/fn/parse-float
core-js(/library)/fn/parse-int

Modules es6.math.acosh, es6.math.asinh, es6.math.atanh, es6.math.cbrt, es6.math.clz32, es6.math.cosh, es6.math.expm1, es6.math.fround, es6.math.hypot, es6.math.imul, es6.math.log10, es6.math.log1p, es6.math.log2, es6.math.sign, es6.math.sinh, es6.math.tanh, es6.math.trunc.

Math
  .acosh(num)     -> num
  .asinh(num)     -> num
  .atanh(num)     -> num
  .cbrt(num)      -> num
  .clz32(num)     -> uint
  .cosh(num)      -> num
  .expm1(num)     -> num
  .fround(num)    -> num
  .hypot(...args) -> num
  .imul(num, num) -> int
  .log1p(num)     -> num
  .log10(num)     -> num
  .log2(num)      -> num
  .sign(num)      -> 1 | -1 | 0 | -0 | NaN
  .sinh(num)      -> num
  .tanh(num)      -> num
  .trunc(num)     -> num

CommonJS entry points:

core-js(/library)/es6/math
core-js(/library)/fn/math/acosh
core-js(/library)/fn/math/asinh
core-js(/library)/fn/math/atanh
core-js(/library)/fn/math/cbrt
core-js(/library)/fn/math/clz32
core-js(/library)/fn/math/cosh
core-js(/library)/fn/math/expm1
core-js(/library)/fn/math/fround
core-js(/library)/fn/math/hypot
core-js(/library)/fn/math/imul
core-js(/library)/fn/math/log1p
core-js(/library)/fn/math/log10
core-js(/library)/fn/math/log2
core-js(/library)/fn/math/sign
core-js(/library)/fn/math/sinh
core-js(/library)/fn/math/tanh
core-js(/library)/fn/math/trunc

Modules es6.date.to-string, ES5 features with fixes: es6.date.now, es6.date.to-iso-string, es6.date.to-json and es6.date.to-primitive.

Date
  .now()               -> int
  #toISOString()       -> string
  #toJSON()            -> string
  #toString()          -> string
  #@@toPrimitive(hint) -> primitive

CommonJS entry points:

core-js/es6/date
core-js/fn/date/to-string
core-js(/library)/fn/date/now
core-js(/library)/fn/date/to-iso-string
core-js(/library)/fn/date/to-json
core-js(/library)/fn/date/to-primitive

Example:

new Date(NaN).toString(); // => 'Invalid Date' 

Module es6.promise.

new Promise(executor(resolve(var), reject(var))) -> promise
  #then(resolved(var), rejected(var))            -> promise
  #catch(rejected(var))                          -> promise
  .resolve(promise | var)                        -> promise
  .reject(var)                                   -> promise
  .all(iterable)                                 -> promise
  .race(iterable)                                -> promise

CommonJS entry points:

core-js(/library)/es6/promise
core-js(/library)/fn/promise

Basic example:

function sleepRandom(time){
  return new Promise(function(resolve, reject){
    setTimeout(resolve, time * 1e3, 0 | Math.random() * 1e3);
  });
}
 
console.log('Run');                    // => Run 
sleepRandom(5).then(function(result){
  console.log(result);                 // => 869, after 5 sec. 
  return sleepRandom(10);
}).then(function(result){
  console.log(result);                 // => 202, after 10 sec. 
}).then(function(){
  console.log('immediately after');    // => immediately after 
  throw Error('Irror!');
}).then(function(){
  console.log('will not be displayed');
}).catch(x => console.log(x));         // => => Error: Irror! 

Promise.resolve and Promise.reject example:

Promise.resolve(42).then(x => console.log(x)); // => 42 
Promise.reject(42).catch(x => console.log(x)); // => 42 
 
Promise.resolve($.getJSON('/data.json')); // => ES6 promise 

Promise.all example:

Promise.all([
  'foo',
  sleepRandom(5),
  sleepRandom(15),
  sleepRandom(10)             // after 15 sec: 
]).then(x => console.log(x)); // => ['foo', 956, 85, 382] 

Promise.race example:

function timeLimit(promise, time){
  return Promise.race([promise, new Promise(function(resolve, reject){
    setTimeout(reject, time * 1e3, Error('Await > ' + time + ' sec'));
  })]);
}
 
timeLimit(sleepRandom(5), 10).then(x => console.log(x));   // => 853, after 5 sec. 
timeLimit(sleepRandom(15), 10).catch(x => console.log(x)); // Error: Await > 10 sec 

ECMAScript 7 async functions example:

var delay = time => new Promise(resolve => setTimeout(resolve, time))
 
async function sleepRandom(time){
  await delay(time * 1e3);
  return 0 | Math.random() * 1e3;
};
async function sleepError(time, msg){
  await delay(time * 1e3);
  throw Error(msg);
};
 
(async () => {
  try {
    console.log('Run');                // => Run 
    console.log(await sleepRandom(5)); // => 936, after 5 sec. 
    var [a, b, c] = await Promise.all([
      sleepRandom(5),
      sleepRandom(15),
      sleepRandom(10)
    ]);
    console.log(a, b, c);              // => 210 445 71, after 15 sec. 
    await sleepError(5, 'Irror!');
    console.log('Will not be displayed');
  } catch(e){
    console.log(e);                    // => Error: 'Irror!', after 5 sec. 
  }
})();

In Node.js, like in native implementation, available events unhandledRejection and rejectionHandled:

process.on('unhandledRejection', (reason, promise) => console.log('unhandled', reason, promise));
process.on('rejectionHandled', (promise) => console.log('handled', promise));
 
var p = Promise.reject(42);
// unhandled 42 [object Promise] 
 
setTimeout(() => p.catch(_ => _), 1e3);
// handled [object Promise] 

In a browser on rejection, by default, you will see notify in the console, or you can add a custom handler and a handler on handling unhandled, example:

window.onunhandledrejection = e => console.log('unhandled', e.reason, e.promise);
window.onrejectionhandled = e => console.log('handled', e.reason, e.promise);
 
var p = Promise.reject(42);
// unhandled 42 [object Promise] 
 
setTimeout(() => p.catch(_ => _), 1e3);
// handled 42 [object Promise] 

Module es6.symbol.

Symbol(description?)  -> symbol
  .hasInstance        -> @@hasInstance
  .isConcatSpreadable -> @@isConcatSpreadable
  .iterator           -> @@iterator
  .match              -> @@match
  .replace            -> @@replace
  .search             -> @@search
  .species            -> @@species
  .split              -> @@split
  .toPrimitive        -> @@toPrimitive
  .toStringTag        -> @@toStringTag
  .unscopables        -> @@unscopables
  .for(key)           -> symbol
  .keyFor(symbol)     -> key
  .useSimple()        -> void
  .useSetter()        -> void
Object
  .getOwnPropertySymbols(object) -> array

Also wrapped some methods for correct work with Symbol polyfill.

Object
  .create(proto | null, descriptors?)    -> object
  .defineProperty(target, key, desc)     -> target
  .defineProperties(target, descriptors) -> target
  .getOwnPropertyDescriptor(var, key)    -> desc | undefined
  .getOwnPropertyNames(var)              -> array
  #propertyIsEnumerable(key)             -> bool
JSON
  .stringify(target, replacer?, space?) -> string | undefined

CommonJS entry points:

core-js(/library)/es6/symbol
core-js(/library)/fn/symbol
core-js(/library)/fn/symbol/has-instance
core-js(/library)/fn/symbol/is-concat-spreadable
core-js(/library)/fn/symbol/iterator
core-js(/library)/fn/symbol/match
core-js(/library)/fn/symbol/replace
core-js(/library)/fn/symbol/search
core-js(/library)/fn/symbol/species
core-js(/library)/fn/symbol/split
core-js(/library)/fn/symbol/to-primitive
core-js(/library)/fn/symbol/to-string-tag
core-js(/library)/fn/symbol/unscopables
core-js(/library)/fn/symbol/for
core-js(/library)/fn/symbol/key-for

Basic example:

var Person = (function(){
  var NAME = Symbol('name');
  function Person(name){
    this[NAME] = name;
  }
  Person.prototype.getName = function(){
    return this[NAME];
  };
  return Person;
})();
 
var person = new Person('Vasya');
console.log(person.getName());          // => 'Vasya' 
console.log(person['name']);            // => undefined 
console.log(person[Symbol('name')]);    // => undefined, symbols are uniq 
for(var key in person)console.log(key); // => only 'getName', symbols are not enumerable 

Symbol.for & Symbol.keyFor example:

var symbol = Symbol.for('key');
symbol === Symbol.for('key'); // true 
Symbol.keyFor(symbol);        // 'key' 

Example with methods for getting own object keys:

var O = {a: 1};
Object.defineProperty(O, 'b', {value: 2});
O[Symbol('c')] = 3;
Object.keys(O);                  // => ['a'] 
Object.getOwnPropertyNames(O);   // => ['a', 'b'] 
Object.getOwnPropertySymbols(O); // => [Symbol(c)] 
Reflect.ownKeys(O);              // => ['a', 'b', Symbol(c)] 
  • We can't add new primitive type, Symbol returns object.
  • Symbol.for and Symbol.keyFor can't be shimmed cross-realm.
  • By default, to hide the keys, Symbol polyfill defines setter in Object.prototype. For this reason, uncontrolled creation of symbols can cause memory leak and the in operator is not working correctly with Symbol polyfill: Symbol() in {} // => true.

You can disable defining setters in Object.prototype. Example:

Symbol.useSimple();
var s1 = Symbol('s1')
  , o1 = {};
o1[s1] = true;
for(var key in o1)console.log(key); // => 'Symbol(s1)_t.qamkg9f3q', w/o native Symbol 
 
Symbol.useSetter();
var s2 = Symbol('s2')
  , o2 = {};
o2[s2] = true;
for(var key in o2)console.log(key); // nothing 
  • Currently, core-js not adds setters to Object.prototype for well-known symbols for correct work something like Symbol.iterator in foo. It can cause problems with their enumerability.
  • Some problems possible with environment exotic objects (for example, IE localStorage).

core-js uses native collections in most case, just fixes methods / constructor, if it's required, and in old environment uses fast polyfill (O(1) lookup).

Module es6.map.

new Map(iterable (entries) ?)     -> map
  #clear()                        -> void
  #delete(key)                    -> bool
  #forEach(fn(val, key, @), that) -> void
  #get(key)                       -> val
  #has(key)                       -> bool
  #set(key, val)                  -> @
  #size                           -> uint
  #values()                       -> iterator
  #keys()                         -> iterator
  #entries()                      -> iterator
  #@@iterator()                   -> iterator (entries)

CommonJS entry points:

core-js(/library)/es6/map
core-js(/library)/fn/map

Examples:

var a = [1];
 
var map = new Map([['a', 1], [42, 2]]);
map.set(a, 3).set(true, 4);
 
console.log(map.size);        // => 4 
console.log(map.has(a));      // => true 
console.log(map.has([1]));    // => false 
console.log(map.get(a));      // => 3 
map.forEach(function(val, key){
  console.log(val);           // => 1, 2, 3, 4 
  console.log(key);           // => 'a', 42, [1], true 
});
map.delete(a);
console.log(map.size);        // => 3 
console.log(map.get(a));      // => undefined 
console.log(Array.from(map)); // => [['a', 1], [42, 2], [true, 4]] 
 
var map = new Map([['a', 1], ['b', 2], ['c', 3]]);
 
for(var [key, val] of map){
  console.log(key);                           // => 'a', 'b', 'c' 
  console.log(val);                           // => 1, 2, 3 
}
for(var val of map.values())console.log(val); // => 1, 2, 3 
for(var key of map.keys())console.log(key);   // => 'a', 'b', 'c' 
for(var [key, val] of map.entries()){
  console.log(key);                           // => 'a', 'b', 'c' 
  console.log(val);                           // => 1, 2, 3 
}

Module es6.set.

new Set(iterable?)              -> set
  #add(key)                     -> @
  #clear()                      -> void
  #delete(key)                  -> bool
  #forEach(fn(el, el, @), that) -> void
  #has(key)                     -> bool
  #size                         -> uint
  #values()                     -> iterator
  #keys()                       -> iterator
  #entries()                    -> iterator
  #@@iterator()                 -> iterator (values)

CommonJS entry points:

core-js(/library)/es6/set
core-js(/library)/fn/set

Examples:

var set = new Set(['a', 'b', 'a', 'c']);
set.add('d').add('b').add('e');
console.log(set.size);        // => 5 
console.log(set.has('b'));    // => true 
set.forEach(function(it){
  console.log(it);            // => 'a', 'b', 'c', 'd', 'e' 
});
set.delete('b');
console.log(set.size);        // => 4 
console.log(set.has('b'));    // => false 
console.log(Array.from(set)); // => ['a', 'c', 'd', 'e'] 
 
var set = new Set([1, 2, 3, 2, 1]);
 
for(var val of set)console.log(val);          // => 1, 2, 3 
for(var val of set.values())console.log(val); // => 1, 2, 3 
for(var key of set.keys())console.log(key);   // => 1, 2, 3 
for(var [key, val] of set.entries()){
  console.log(key);                           // => 1, 2, 3 
  console.log(val);                           // => 1, 2, 3 
}

Module es6.weak-map.

new WeakMap(iterable (entries) ?) -> weakmap
  #delete(key)                    -> bool
  #get(key)                       -> val
  #has(key)                       -> bool
  #set(key, val)                  -> @

CommonJS entry points:

core-js(/library)/es6/weak-map
core-js(/library)/fn/weak-map

Examples:

var a = [1]
  , b = [2]
  , c = [3];
 
var wmap = new WeakMap([[a, 1], [b, 2]]);
wmap.set(c, 3).set(b, 4);
console.log(wmap.has(a));   // => true 
console.log(wmap.has([1])); // => false 
console.log(wmap.get(a));   // => 1 
wmap.delete(a);
console.log(wmap.get(a));   // => undefined 
 
// Private properties store: 
var Person = (function(){
  var names = new WeakMap;
  function Person(name){
    names.set(this, name);
  }
  Person.prototype.getName = function(){
    return names.get(this);
  };
  return Person;
})();
 
var person = new Person('Vasya');
console.log(person.getName());          // => 'Vasya' 
for(var key in person)console.log(key); // => only 'getName' 

Module es6.weak-set.

new WeakSet(iterable?) -> weakset
  #add(key)            -> @
  #delete(key)         -> bool
  #has(key)            -> bool

CommonJS entry points:

core-js(/library)/es6/weak-set
core-js(/library)/fn/weak-set

Examples:

var a = [1]
  , b = [2]
  , c = [3];
 
var wset = new WeakSet([a, b, a]);
wset.add(c).add(b).add(c);
console.log(wset.has(b));   // => true 
console.log(wset.has([2])); // => false 
wset.delete(b);
console.log(wset.has(b));   // => false 
  • Weak-collections polyfill stores values as hidden properties of keys. It works correct and not leak in most cases. However, it is desirable to store a collection longer than its keys.

Implementations and fixes ArrayBuffer, DataView, typed arrays constructors, static and prototype methods. Typed Arrays work only in environments with support descriptors (IE9+), ArrayBuffer and DataView should work anywhere.

Modules es6.typed.array-buffer, es6.typed.data-view, es6.typed.int8-array, es6.typed.uint8-array, es6.typed.uint8-clamped-array, es6.typed.int16-array, es6.typed.uint16-array, es6.typed.int32-array, es6.typed.uint32-array, es6.typed.float32-array and es6.typed.float64-array.

new ArrayBuffer(length) -> buffer
  .isView(var) -> bool
  #slice(start = 0, end = @length) -> buffer
  #byteLength -> uint
 
new DataView(buffer, byteOffset = 0, byteLength = buffer.byteLength - byteOffset) -> view
  #getInt8(offset)                          -> int8
  #getUint8(offset)                         -> uint8
  #getInt16(offset, littleEndian = false)   -> int16
  #getUint16(offset, littleEndian = false)  -> uint16
  #getInt32(offset, littleEndian = false)   -> int32
  #getUint32(offset, littleEndian = false)  -> uint32
  #getFloat32(offset, littleEndian = false) -> float32
  #getFloat64(offset, littleEndian = false) -> float64
  #setInt8(offset, value)                          -> void
  #setUint8(offset, value)                         -> void
  #setInt16(offset, value, littleEndian = false)   -> void
  #setUint16(offset, value, littleEndian = false)  -> void
  #setInt32(offset, value, littleEndian = false)   -> void
  #setUint32(offset, value, littleEndian = false)  -> void
  #setFloat32(offset, value, littleEndian = false) -> void
  #setFloat64(offset, value, littleEndian = false) -> void
  #buffer     -> buffer
  #byteLength -> uint
  #byteOffset -> uint
 
{
  Int8Array,
  Uint8Array,
  Uint8ClampedArray,
  Int16Array,
  Uint16Array,
  Int32Array,
  Uint32Array,
  Float32Array,
  Float64Array
}
  new %TypedArray%(length)    -> typed
  new %TypedArray%(typed)     -> typed
  new %TypedArray%(arrayLike) -> typed
  new %TypedArray%(iterable)  -> typed
  new %TypedArray%(buffer, byteOffset = 0, length = (buffer.byteLength - byteOffset) / @BYTES_PER_ELEMENT) -> typed
  .BYTES_PER_ELEMENT -> uint
  .from(arrayLike | iterable, mapFn(val, index)?, that) -> typed
  .of(...args) -> typed
  #BYTES_PER_ELEMENT -> uint
  #copyWithin(target = 0, start = 0, end = @length) -> @
  #every(fn(val, index, @), that) -> bool
  #fill(val, start = 0, end = @length) -> @
  #filter(fn(val, index, @), that) -> typed
  #find(fn(val, index, @), that) -> val
  #findIndex(fn(val, index, @), that) -> index
  #forEach(fn(val, index, @), that) -> void
  #indexOf(var, from?) -> int
  #join(string = ',') -> string
  #lastIndexOf(var, from?) -> int
  #map(fn(val, index, @), that) -> typed
  #reduce(fn(memo, val, index, @), memo?) -> var
  #reduceRight(fn(memo, val, index, @), memo?) -> var
  #reverse() -> @
  #set(arrayLike, offset = 0) -> void
  #slice(start = 0, end = @length) -> typed
  #some(fn(val, index, @), that) -> bool
  #sort(fn(a, b)?) -> @
  #subarray(start = 0, end = @length) -> typed
  #toString() -> string
  #toLocaleString() -> string
  #values()     -> iterator
  #keys()       -> iterator
  #entries()    -> iterator
  #@@iterator() -> iterator (values)
  #buffer     -> buffer
  #byteLength -> uint
  #byteOffset -> uint
  #length     -> uint

CommonJS entry points:

core-js(/library)/es6/typed
core-js(/library)/fn/typed
core-js(/library)/fn/typed/array-buffer
core-js(/library)/fn/typed/data-view
core-js(/library)/fn/typed/int8-array
core-js(/library)/fn/typed/uint8-array
core-js(/library)/fn/typed/uint8-clamped-array
core-js(/library)/fn/typed/int16-array
core-js(/library)/fn/typed/uint16-array
core-js(/library)/fn/typed/int32-array
core-js(/library)/fn/typed/uint32-array
core-js(/library)/fn/typed/float32-array
core-js(/library)/fn/typed/float64-array

Examples:

new Int32Array(4);                          // => [0, 0, 0, 0] 
new Uint8ClampedArray([1, 2, 3, 666]);      // => [1, 2, 3, 255] 
new Float32Array(new Set([1, 2, 3, 2, 1])); // => [1, 2, 3] 
 
var buffer = new ArrayBuffer(8);
var view   = new DataView(buffer);
view.setFloat64(0, 123.456, true);
new Uint8Array(buffer.slice(4)); // => [47, 221, 94, 64] 
 
Int8Array.of(1, 1.5, 5.7, 745);      // => [1, 1, 5, -23] 
Uint8Array.from([1, 1.5, 5.7, 745]); // => [1, 1, 5, 233] 
 
var typed = new Uint8Array([1, 2, 3]);
 
var a = typed.slice(1);    // => [2, 3] 
typed.buffer === a.buffer; // => false 
var b = typed.subarray(1); // => [2, 3] 
typed.buffer === b.buffer; // => true 
 
typed.filter(it => it % 2); // => [1, 3] 
typed.map(it => it * 1.5);  // => [1, 3, 4] 
 
for(var val of typed)console.log(val);          // => 1, 2, 3 
for(var val of typed.values())console.log(val); // => 1, 2, 3 
for(var key of typed.keys())console.log(key);   // => 0, 1, 2 
for(var [key, val] of typed.entries()){
  console.log(key);                             // => 0, 1, 2 
  console.log(val);                             // => 1, 2, 3 
}
  • Typed Arrays polyfills works completely how should work by the spec, but because of internal use getter / setters on each instance, is slow and consumes significant memory. However, typed arrays polyfills required mainly for IE9 (and for Uint8ClampedArray in IE10 and early IE11), all modern engines have native typed arrays and requires only constructors fixes and methods.
  • The current version hasn't special entry points for methods, they can be added only with constructors. It can be added in the future.
  • In the library version we can't pollute native prototypes, so prototype methods available as constructors static.

Modules es6.reflect.apply, es6.reflect.construct, es6.reflect.define-property, es6.reflect.delete-property, es6.reflect.enumerate, es6.reflect.get, es6.reflect.get-own-property-descriptor, es6.reflect.get-prototype-of, es6.reflect.has, es6.reflect.is-extensible, es6.reflect.own-keys, es6.reflect.prevent-extensions, es6.reflect.set, es6.reflect.set-prototype-of.

Reflect
  .apply(target, thisArgument, argumentsList) -> var
  .construct(target, argumentsList, newTarget?) -> object
  .defineProperty(target, propertyKey, attributes) -> bool
  .deleteProperty(target, propertyKey) -> bool
  .enumerate(target) -> iterator (removed from the spec and will be removed from core-js@3)
  .get(target, propertyKey, receiver?) -> var
  .getOwnPropertyDescriptor(target, propertyKey) -> desc
  .getPrototypeOf(target) -> object | null
  .has(target, propertyKey) -> bool
  .isExtensible(target) -> bool
  .ownKeys(target) -> array
  .preventExtensions(target) -> bool
  .set(target, propertyKey, V, receiver?) -> bool
  .setPrototypeOf(target, proto) -> bool (required __proto__ - IE11+)

CommonJS entry points:

core-js(/library)/es6/reflect
core-js(/library)/fn/reflect
core-js(/library)/fn/reflect/apply
core-js(/library)/fn/reflect/construct
core-js(/library)/fn/reflect/define-property
core-js(/library)/fn/reflect/delete-property
core-js(/library)/fn/reflect/enumerate (deprecated and will be removed from the next major release)
core-js(/library)/fn/reflect/get
core-js(/library)/fn/reflect/get-own-property-descriptor
core-js(/library)/fn/reflect/get-prototype-of
core-js(/library)/fn/reflect/has
core-js(/library)/fn/reflect/is-extensible
core-js(/library)/fn/reflect/own-keys
core-js(/library)/fn/reflect/prevent-extensions
core-js(/library)/fn/reflect/set
core-js(/library)/fn/reflect/set-prototype-of

Examples:

var O = {a: 1};
Object.defineProperty(O, 'b', {value: 2});
O[Symbol('c')] = 3;
Reflect.ownKeys(O); // => ['a', 'b', Symbol(c)] 
 
function C(a, b){
  this.c = a + b;
}
 
var instance = Reflect.construct(C, [20, 22]);
instance.c; // => 42 

The TC39 process.

CommonJS entry points:

core-js(/library)/es7
core-js(/library)/es7/array
core-js(/library)/es7/string
core-js(/library)/es7/map
core-js(/library)/es7/set
core-js(/library)/es7/error
core-js(/library)/es7/math
core-js(/library)/es7/system
core-js(/library)/es7/symbol
core-js(/library)/es7/reflect
core-js(/library)/es7/observable

core-js/stage/4 entry point contains only stage 4 proposals, core-js/stage/3 - stage 3 and stage 4, etc.

CommonJS entry points:

core-js(/library)/stage/4
Array
  #includes(var, from?) -> bool
{
  Int8Array,
  Uint8Array,
  Uint8ClampedArray,
  Int16Array,
  Uint16Array,
  Int32Array,
  Uint32Array,
  Float32Array,
  Float64Array
}
  #includes(var, from?) -> bool

CommonJS entry points:

core-js(/library)/fn/array/includes

Examples:

[1, 2, 3].includes(2);        // => true 
[1, 2, 3].includes(4);        // => false 
[1, 2, 3].includes(2, 2);     // => false 
 
[NaN].indexOf(NaN);           // => -1 
[NaN].includes(NaN);          // => true 
Array(1).indexOf(undefined);  // => -1 
Array(1).includes(undefined); // => true 
Object
  .values(object) -> array
  .entries(object) -> array

CommonJS entry points:

core-js(/library)/fn/object/values
core-js(/library)/fn/object/entries

Examples:

Object.values({a: 1, b: 2, c: 3});  // => [1, 2, 3] 
Object.entries({a: 1, b: 2, c: 3}); // => [['a', 1], ['b', 2], ['c', 3]] 
 
for(let [key, value] of Object.entries({a: 1, b: 2, c: 3})){
  console.log(key);   // => 'a', 'b', 'c' 
  console.log(value); // => 1, 2, 3 
}
Object
  #__defineSetter__(key, fn) -> void
  #__defineGetter__(key, fn) -> void
  #__lookupSetter__(key) -> fn | void
  #__lookupGetter__(key) -> fn | void

CommonJS entry points:

core-js(/library)/fn/object/define-getter
core-js(/library)/fn/object/define-setter
core-js(/library)/fn/object/lookup-getter
core-js(/library)/fn/object/lookup-setter

CommonJS entry points:

core-js(/library)/stage/3
Object
  .getOwnPropertyDescriptors(object) -> object

CommonJS entry points:

core-js(/library)/fn/object/get-own-property-descriptors

Examples:

// Shallow object cloning with prototype and descriptors: 
var copy = Object.create(Object.getPrototypeOf(O), Object.getOwnPropertyDescriptors(O));
// Mixin: 
Object.defineProperties(target, Object.getOwnPropertyDescriptors(source));
String
  #padStart(length,