core-js

Modular compact standard library for JavaScript. Includes polyfills for ECMAScript 5, ECMAScript 6: symbols, collections, iterators, promises, ECMAScript 7 proposals; setImmediate, array generics. Some additional features such as dictionaries or extended partial application. You can require only standardized features polyfills, use features without global namespace pollution or create a custom build.

Example:

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

• Usage
  • Basic
  • CommonJS
  • Custom build
• Features
  • ECMAScript 5
  • ECMAScript 6
    • ECMAScript 6: Object
    • ECMAScript 6: Function
    • ECMAScript 6: Array
    • ECMAScript 6: String
    • ECMAScript 6: RegExp
    • ECMAScript 6: Number
    • ECMAScript 6: Math
    • ECMAScript 6: Symbol
    • ECMAScript 6: Collections
    • ECMAScript 6: Iterators
    • ECMAScript 6: Promise
    • ECMAScript 6: Reflect
  • ECMAScript 7
  • Mozilla JavaScript: Array generics
  • Web standards
    • setTimeout / setInterval
    • setImmediate
  • Non-standard
    • Object
    • Dict
    • Partial application
    • Number Iterator
    • Escaping HTML
    • delay
    • console
• Missing polyfills
• Changelog

Usage

Basic

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: default, without global namespace pollution, shim only.

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

CommonJS

You can require only needed modules.

require('core-js/es5'); // if you need support IE8-
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 core      = require('core-js/library/es5'); // if you need support IE8-
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, excluding features from es5 module (this module requires completely in ES3 environment before all other modules).

Available 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.

Custom build

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.

Available custom build from js code (required webpack):

require('core-js/build')({
  modules: ['es6', 'core.dict'], // modules / namespaces
  blacklist: ['es6.reflect'],    // blacklist of modules / namespaces
  library: false,                // flag for build without global namespace pollution
}, function(err, code){          // callback
  // ...
});

Features:

ECMAScript 5

Module es5, nothing new - without examples.

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
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
Function
  #bind(object, ...args) -> boundFn(...args)
Date
  .now() -> int
  #toISOString() -> string

Some features moved to another modules / namespaces, but available as part of es5 namespace too:

Object
  .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-
String
  #trim() -> str

ECMAScript 6

ECMAScript 6: Object

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

Object
  .assign(target, ...src) -> target
  .is(a, b) -> bool
  .setPrototypeOf(target, proto | null) -> target (required __proto__ - IE11+)
  #toString() -> string, ES6 fix: @@toStringTag support

Example:

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]'

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, es6.object.get-own-property-names.

Object
  .freeze(var) -> var
  .seal(var) -> var
  .preventExtensions(var) -> var
  .isFrozen(var) -> bool
  .isSealed(var) -> bool
  .isExtensible(var) -> bool
  .getOwnPropertyDescriptor(var, key) -> desc | undefined
  .getPrototypeOf(var) -> object | null
  .keys(var) -> array
  .getOwnPropertyNames(var) -> array

Example:

Object.keys('qwe'); // => ['0', '1', '2']
Object.getPrototypeOf('qwe') === String.prototype; // => true

ECMAScript 6: Function

Modules es6.function.name and es6.function.has-instance.

Function
  #name -> string (IE9+)
  #@@hasInstance(var) -> bool

Example:

(function foo(){}).name // => 'foo'

ECMAScript 6: Array

Modules es6.array.from, es6.array.of, es6.array.copy-within, es6.array.fill, es6.array.find and es6.array.find-index.

Array
  .from(iterable | array-like, mapFn(val, index)?, that) -> array
  .of(...args) -> array
  #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
  #@@unscopables -> object (cap)

Example:

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]

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]

ECMAScript 6: String

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

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

Examples:

'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'

ECMAScript 6: RegExp

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.

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
[new] RegExp(pattern, flags?) -> regexp, ES6 fix: can alter flags (IE9+)
  #flags -> str (IE9+)
  #@@match(str) -> array | null
  #@@replace(str, replacer) -> string
  #@@search(str) -> index
  #@@split(str, limit) -> array

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

ECMAScript 6: Number

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

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

Number: 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.

[new] Number(var) -> number | number object
  .EPSILON -> num
  .isFinite(num) -> bool
  .isInteger(num) -> bool
  .isNaN(num) -> bool
  .isSafeInteger(num) -> bool
  .MAX_SAFE_INTEGER -> int
  .MIN_SAFE_INTEGER -> int
  .parseFloat(str) -> num
  .parseInt(str) -> int

ECMAScript 6: Math

Math: 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

ECMAScript 6: Symbol

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

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');
log(person.getName());          // => 'Vasya'
log(person['name']);            // => undefined
log(person[Symbol('name')]);    // => undefined, symbols are uniq
for(var key in person)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)]

Caveats when using Symbol polyfill:

• 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)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)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.

ECMAScript 6: Collections

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).

Map

Module es6.map. About iterators from this module here.

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

Example:

var a = [1];

var map = new Map([['a', 1], [42, 2]]);
map.set(a, 3).set(true, 4);

log(map.size);        // => 4
log(map.has(a));      // => true
log(map.has([1]));    // => false
log(map.get(a));      // => 3
map.forEach(function(val, key){
  log(val);           // => 1, 2, 3, 4
  log(key);           // => 'a', 42, [1], true
});
map.delete(a);
log(map.size);        // => 3
log(map.get(a));      // => undefined
log(Array.from(map)); // => [['a', 1], [42, 2], [true, 4]]

Set

Module es6.set. About iterators from this module here.

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

Example:

var set = new Set(['a', 'b', 'a', 'c']);
set.add('d').add('b').add('e');
log(set.size);        // => 5
log(set.has('b'));    // => true
set.forEach(function(it){
  log(it);            // => 'a', 'b', 'c', 'd', 'e'
});
set.delete('b');
log(set.size);        // => 4
log(set.has('b'));    // => false
log(Array.from(set)); // => ['a', 'c', 'd', 'e']

WeakMap

Module es6.weak-map.

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

Example:

var a = [1]
  , b = [2]
  , c = [3];

var wmap = new WeakMap([[a, 1], [b, 2]]);
wmap.set(c, 3).set(b, 4);
log(wmap.has(a));   // => true
log(wmap.has([1])); // => false
log(wmap.get(a));   // => 1
wmap.delete(a);
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');
log(person.getName());          // => 'Vasya'
for(var key in person)log(key); // => only 'getName'

WeakSet

Module es6.weak-set.

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

Example:

var a = [1]
  , b = [2]
  , c = [3];

var wset = new WeakSet([a, b, a]);
wset.add(c).add(b).add(c);
log(wset.has(b));   // => true
log(wset.has([2])); // => false
wset.delete(b);
log(wset.has(b));   // => false

Caveats when using collections polyfill:

• Frozen objects as collection keys are supported, but not recomended - it's slow (O(n) instead of O(1)) and, for weak-collections, leak.
• 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.

ECMAScript 6: Iterators

Modules es6.string.iterator and es6.array.iterator:

String
  #@@iterator() -> iterator
Array
  #values() -> iterator
  #keys() -> iterator
  #entries() -> iterator (entries)
  #@@iterator() -> iterator
Arguments
  #@@iterator() -> iterator (available only in core-js methods)

Modules es6.map and es6.set:

Map
  #values() -> iterator
  #keys() -> iterator
  #entries() -> iterator (entries)
  #@@iterator() -> iterator (entries)
Set
  #values() -> iterator
  #keys() -> iterator
  #entries() -> iterator (entries)
  #@@iterator() -> iterator

Module web.dom.iterable:

NodeList
  #@@iterator() -> iterator

Example:

var string = 'a𠮷b';

for(var val of string)log(val);         // => 'a', '𠮷', 'b'

var array = ['a', 'b', 'c'];

for(var val of array)log(val);          // => 'a', 'b', 'c'
for(var val of array.values())log(val); // => 'a', 'b', 'c'
for(var key of array.keys())log(key);   // => 0, 1, 2
for(var [key, val] of array.entries()){
  log(key);                             // => 0, 1, 2
  log(val);                             // => 'a', 'b', 'c'
}

var map = new Map([['a', 1], ['b', 2], ['c', 3]]);

for(var [key, val] of map){
  log(key);                             // => 'a', 'b', 'c'
  log(val);                             // => 1, 2, 3
}
for(var val of map.values())log(val);   // => 1, 2, 3
for(var key of map.keys())log(key);     // => 'a', 'b', 'c'
for(var [key, val] of map.entries()){
  log(key);                             // => 'a', 'b', 'c'
  log(val);                             // => 1, 2, 3
}

var set = new Set([1, 2, 3, 2, 1]);

for(var val of set)log(val);            // => 1, 2, 3
for(var val of set.values())log(val);   // => 1, 2, 3
for(var key of set.keys())log(key);     // => 1, 2, 3
for(var [key, val] of set.entries()){
  log(key);                             // => 1, 2, 3
  log(val);                             // => 1, 2, 3
}

for(var x of document.querySelectorAll('*')){
  log(x.id);
}

Modules core.is-iterable, core.get-iterator, core.get-iterator-method - helpers for check iterable / get iterator in library version or, for example, for arguments object:

core
  .isIterable(var) -> bool
  .getIterator(iterable) -> iterator
  .getIteratorMethod(var) -> function | undefined

Example:

var list = (function(){
  return arguments;
})(1, 2, 3);

log(core.isIterable(list)); // true;

var iter = core.getIterator(list);
log(iter.next().value); // 1
log(iter.next().value); // 2
log(iter.next().value); // 3
log(iter.next().value); // undefined

core.getIterator({});   // TypeError: [object Object] is not iterable!

var iterFn = core.getIteratorMethod(list);
log(typeof iterFn);     // 'function'
var iter = iterFn.call(list);
log(iter.next().value); // 1
log(iter.next().value); // 2
log(iter.next().value); // 3
log(iter.next().value); // undefined

log(core.getIteratorMethod({})); // undefined

ECMAScript 6: Promise

Module es6.promise.

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

Basic example:

function sleepRandom(time){
  return new Promise(function(resolve, reject){
    setTimeout(resolve, time * 1e3, 0 | Math.random() * 1e3);
  });
}

log('Run');                    // => Run
sleepRandom(5).then(function(result){
  log(result);                 // => 869, after 5 sec.
  return sleepRandom(10);
}).then(function(result){
  log(result);                 // => 202, after 10 sec.
}).then(function(){
  log('immediately after');    // => immediately after
  throw Error('Irror!');
}).then(function(){
  log('will not be displayed');
}).catch(log);                 // => => Error: Irror!

Promise.resolve and Promise.reject example:

Promise.resolve(42).then(log); // => 42
Promise.reject(42).catch(log); // => 42

Promise.resolve($.getJSON('/data.json')); // => ES6 promise

Promise.all example:

Promise.all([
  'foo',
  sleepRandom(5),
  sleepRandom(15),
  sleepRandom(10)  // after 15 sec:
]).then(log);      // => ['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(log);   // => 853, after 5 sec.
timeLimit(sleepRandom(15), 10).catch(log); // 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 {
    log('Run');                // => Run
    log(await sleepRandom(5)); // => 936, after 5 sec.
    var [a, b, c] = await Promise.all([
      sleepRandom(5),
      sleepRandom(15),
      sleepRandom(10)
    ]);
    log(a, b, c);              // => 210 445 71, after 15 sec.
    await sleepError(5, 'Irror!');
    log('Will not be displayed');
  } catch(e){
    log(e);                    // => Error: 'Irror!', after 5 sec.
  }
})();

Unhandled rejection tracking

core-js Promise supports (but not adds to native implementations) unhandled rejection tracking.

Node.js:

process.on('unhandledRejection', (reason, promise) => console.log(reason, promise));
Promise.reject(42);
// 42 [object Promise]

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

window.onunhandledrejection = e => log(e.reason, e.promise);
Promise.reject(42);
// 42 [object Promise]

Warning: The problem here - we can't add it to native Promise implementations, but by idea core-js should use enough correct native implementation if it's available. Currently, most native implementations are buggy and core-js uses polyfill, but the situation will be changed. If someone wanna use this hook everywhere - he should delete window.Promise before inclusion core-js.

ECMAScript 6: Reflect

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
  .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+)

Example:

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

ECMAScript 7

• Array#includes proposal - module es7.array.includes
• String#at proposal - module es7.string.at
• String#padLeft, String#padRight proposal - modules es7.string.pad-left, es7.string.pad-right
• String#trimLeft, String#trimRight proposal - modules es7.string.trim-left, es7.string.trim-right
• Object.values, Object.entries proposal - modules es7.object.values, es7.object.entries
• Object.getOwnPropertyDescriptors proposal - module es7.object.get-own-property-descriptors
• RegExp.escape proposal - module es7.regexp.escape
• Map#toJSON, Set#toJSON proposal - modules es7.map.to-json, es7.set.to-json

Array
  #includes(var, from?) -> bool
String
  #at(index) -> string
  #padLeft(length, fillStr = ' ') -> string
  #padRight(length, fillStr = ' ') -> string
  #trimLeft() -> string
  #trimRight() -> string
Object
  .values(object) -> array
  .entries(object) -> array
  .getOwnPropertyDescriptors(object) -> object
RegExp
  .escape(str) -> str
Map
  #toJSON() -> array
Set
  #toJSON() -> array

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

'a𠮷b'.at(1);        // => '𠮷'
'a𠮷b'.at(1).length; // => 2

'hello'.padLeft(10);          // => '     hello'
'hello'.padLeft(10, '1234');  // => '41234hello'
'hello'.padRight(10);         // => 'hello     '
'hello'.padRight(10, '1234'); // => 'hello12341'

'   hello   '.trimLeft();  // => 'hello   '
'   hello   '.trimRight(); // => '   hello'

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]]

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

RegExp.escape('Hello, []{}()*+?.\\^$|!'); // => 'Hello, \[\]\{\}\(\)\*\+\?\.\\\^\$\|!'

JSON.stringify(new Map([['a', 'b'], ['c', 'd']])); // => '[["a","b"],["c","d"]]'
JSON.stringify(new Set([1, 2, 3, 2, 1]));          // => '[1,2,3]'

Mozilla JavaScript: Array generics

Module js.array.statics.

Array
  .{...ArrayPrototype methods}

Array.slice(arguments, 1);

Array.join('abcdef', '+'); // => 'a+b+c+d+e+f'

var form = document.getElementsByClassName('form__input');
Array.reduce(form, function(memo, it){
  memo[it.name] = it.value;
  return memo;
}, {}); // => {name: 'Vasya', age: '42', sex: 'yes, please'}

Web standards

setTimeout / setInterval

Module web.timers. Additional arguments fix for IE9-.

setTimeout(fn(...args), time, ...args) -> id
setInterval(fn(...args), time, ...args) -> id

// Before:
setTimeout(log.bind(null, 42), 1000);
// After:
setTimeout(log, 1000, 42);

setImmediate

Module web.immediate. setImmediate proposal polyfill.

setImmediate(fn(...args), ...args) -> id
clearImmediate(id) -> void

Example:

setImmediate(function(arg1, arg2){
  log(arg1, arg2); // => Message will be displayed with minimum delay
}, 'Message will be displayed', 'with minimum delay');

clearImmediate(setImmediate(function(){
  log('Message will not be displayed');
}));

Non-standard

Object

Modules core.object.is-object, core.object.classof, core.object.define, core.object.make.

Object
  .isObject(var) -> bool
  .classof(var) -> string 
  .define(target, mixin) -> target
  .make(proto | null, mixin?) -> object

Object classify examples:

Object.isObject({});    // => true
Object.isObject(isNaN); // => true
Object.isObject(null);  // => false

var classof = Object.classof;

classof(null);                 // => 'Null'
classof(undefined);            // => 'Undefined'
classof(1);                    // => 'Number'
classof(true);                 // => 'Boolean'
classof('string');             // => 'String'
classof(Symbol());             // => 'Symbol'

classof(new Number(1));        // => 'Number'
classof(new Boolean(true));    // => 'Boolean'
classof(new String('string')); // => 'String'

var fn   = function(){}
  , list = (function(){return arguments})(1, 2, 3);

classof({});                   // => 'Object'
classof(fn);                   // => 'Function'
classof([]);                   // => 'Array'
classof(list);                 // => 'Arguments'
classof(/./);                  // => 'RegExp'
classof(new TypeError);        // => 'Error'

classof(new Set);              // => 'Set'
classof(new Map);              // => 'Map'
classof(new WeakSet);          // => 'WeakSet'
classof(new WeakMap);          // => 'WeakMap'
classof(new Promise(fn));      // => 'Promise'

classof([].values());          // => 'Array Iterator'
classof(new Set().values());   // => 'Set Iterator'
classof(new Map().values());   // => 'Map Iterator'

classof(Math);                 // => 'Math'
classof(JSON);                 // => 'JSON'

function Example(){}
Example.prototype[Symbol.toStringTag] = 'Example';

classof(new Example);          // => 'Example'

Object.define and Object.make examples:

// Before:
Object.defineProperty(target, 'c', {
  enumerable: true,
  configurable: true,
  get: function(){
    return this.a + this.b;
  }
});

// After:
Object.define(target, {
  get c(){
    return this.a + this.b;
  }
});

// Shallow object cloning with prototype and descriptors:
var copy = Object.make(Object.getPrototypeOf(src), src);

// Simple inheritance:
function Vector2D(x, y){
  this.x = x;
  this.y = y;
}
Object.define(Vector2D.prototype, {
  get xy(){
    return Math.hypot(this.x, this.y);
  }
});
function Vector3D(x, y, z){
  Vector2D.apply(this, arguments);
  this.z = z;
}
Vector3D.prototype = Object.make(Vector2D.prototype, {
  constructor: Vector3D,
  get xyz(){
    return Math.hypot(this.x, this.y, this.z);
  }
});

var vector = new Vector3D(9, 12, 20);
log(vector.xy);  // => 15
log(vector.xyz); // => 25
vector.y++;
log(vector.xy);  // => 15.811388300841896
log(vector.xyz); // => 25.495097567963924

Dict

Module core.dict. Based on TC39 discuss / strawman.

[new] Dict(iterable (entries) | object ?) -> dict
  .isDict(var) -> bool
  .values(object) -> iterator
  .keys(object) -> iterator
  .entries(object) -> iterator (entries)
  .has(object, key) -> bool
  .get(object, key) -> val
  .set(object, key, value) -> object
  .forEach(object, fn(val, key, @), that) -> void
  .map(object, fn(val, key, @), that) -> new @
  .mapPairs(object, fn(val, key, @), that) -> new @
  .filter(object, fn(val, key, @), that) -> new @
  .some(object, fn(val, key, @), that) -> bool
  .every(object, fn(val, key, @), that) -> bool
  .find(object, fn(val, key, @), that) -> val
  .findKey(object, fn(val, key, @), that) -> key
  .keyOf(object, var) -> key
  .includes(object, var) -> bool
  .reduce(object, fn(memo, val, key, @), memo?) -> var

Dict create object without prototype from iterable or simple object. Example:

var map = new Map([['a', 1], ['b', 2], ['c', 3]]);

Dict();                    // => {__proto__: null}
Dict({a: 1, b: 2, c: 3});  // => {__proto__: null, a: 1, b: 2, c: 3}
Dict(map);                 // => {__proto__: null, a: 1, b: 2, c: 3}
Dict([1, 2, 3].entries()); // => {__proto__: null, 0: 1, 1: 2, 2: 3}

var dict = Dict({a: 42});
dict instanceof Object;   // => false
dict.a;                   // => 42
dict.toString;            // => undefined
'a' in dict;              // => true
'hasOwnProperty' in dict; // => false

Dict.isDict({});     // => false
Dict.isDict(Dict()); // => true

Dict.keys, Dict.values and Dict.entries returns iterators for objects, examples:

var dict = {a: 1, b: 2, c: 3};

for(var key of Dict.keys(dict))log(key); // => 'a', 'b', 'c'

for(var val of Dict.values(dict))log(val); // => 1, 2, 3

for(var [key, val] of Dict.entries(dict)){
  log(key); // => 'a', 'b', 'c'
  log(val); // => 1, 2, 3
}

new Map(Dict.entries(dict)); // => Map {a: 1, b: 2, c: 3}

Basic dict operations for objects with prototype example:

'q' in {q: 1};            // => true
'toString' in {};         // => true

Dict.has({q: 1}, 'q');    // => true
Dict.has({}, 'toString'); // => false

({q: 1})['q'];            // => 1
({}).toString;            // => function toString(){ [native code] }

Dict.get({q: 1}, 'q');    // => 1
Dict.get({}, 'toString'); // => undefined

var O = {};
O['q'] = 1;
O['q'];         // => 1
O['__proto__'] = {w: 2};
O['__proto__']; // => {w: 2}
O['w'];         // => 2

var O = {};
Dict.set(O, 'q', 1);
O['q'];         // => 1
Dict.set(O, '__proto__', {w: 2});
O['__proto__']; // => {w: 2}
O['w'];         // => undefined

Other methods of Dict module are static equialents of Array.prototype methods for dictionaries, examples:

var dict = {a: 1, b: 2, c: 3};

Dict.forEach(dict, console.log, console);
// => 1, 'a', {a: 1, b: 2, c: 3}
// => 2, 'b', {a: 1, b: 2, c: 3}
// => 3, 'c', {a: 1, b: 2, c: 3}

Dict.map(dict, function(it){
  return it * it;
}); // => {a: 1, b: 4, c: 9}

Dict.mapPairs(dict, function(val, key){
  if(key != 'b')return [key + key, val * val];
}); // => {aa: 1, cc: 9}

Dict.filter(dict, function(it){
  return it % 2;
}); // => {a: 1, c: 3}

Dict.some(dict, function(it){
  return it === 2;
}); // => true

Dict.every(dict, function(it){
  return it === 2;
}); // => false

Dict.find(dict, function(it){
  return it > 2;
}); // => 3
Dict.find(dict, function(it){
  return it > 4;
}); // => undefined

Dict.findKey(dict, function(it){
  return it > 2;
}); // => 'c'
Dict.findKey(dict, function(it){
  return it > 4;
}); // => undefined

Dict.keyOf(dict, 2);    // => 'b'
Dict.keyOf(dict, 4);    // => undefined

Dict.includes(dict, 2); // => true
Dict.includes(dict, 4); // => false

Dict.reduce(dict, function(memo, it){
  return memo + it;
});     // => 6
Dict.reduce(dict, function(memo, it){
  return memo + it;
}, ''); // => '123'

Partial application

Module core.function.part.

Function
  #part(...args | _) -> fn(...args)

Function#part partial apply function without this binding. Uses global variable _ (core._ for builds without global namespace pollution) as placeholder and not conflict with Underscore / LoDash. Examples:

var fn1 = log.part(1, 2);
fn1(3, 4);    // => 1, 2, 3, 4

var fn2 = log.part(_, 2, _, 4);
fn2(1, 3);    // => 1, 2, 3, 4

var fn3 = log.part(1, _, _, 4);
fn3(2, 3);    // => 1, 2, 3, 4

fn2(1, 3, 5); // => 1, 2, 3, 4, 5
fn2(1);       // => 1, 2, undefined, 4

Number Iterator

Modules core.number.iterator.

Number
  #@@iterator() -> iterator

Examples:

for(var i of 3)log(i); // => 0, 1, 2

[...10]; // => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Array.from(10, Math.random); // => [0.9817775336559862, 0.02720663254149258, ...]

Array.from(10, function(it){
  return this + it * it;
}, .42); // => [0.42, 1.42, 4.42, 9.42, 16.42, 25.42, 36.42, 49.42, 64.42, 81.42]

Escaping HTML

Modules core.string.escape-html and core.string.unescape-html.

String
  #escapeHTML() -> str
  #unescapeHTML() -> str

Examples:

'<script>doSomething();</script>'.escapeHTML(); // => '&lt;script&gt;doSomething();&lt;/script&gt;'
'&lt;script&gt;doSomething();&lt;/script&gt;'.unescapeHTML(); // => '<script>doSomething();</script>'

delay

Module core.delay. Promise-returning delay function, esdiscuss. Example:

delay(1e3).then(() => log('after 1 sec'));

(async () => {
  await delay(3e3);
  log('after 3 sec');
  
  while(await delay(3e3))log('each 3 sec');
})();

Console

Module core.log. Console cap for old browsers and some additional functionality. In IE, Node.js / IO.js and Firebug console methods not require call from console object, but in Chromium and V8 this throws error. For some reason, we can't replace console methods by their bound versions. Add log object with bound console methods. Some more sugar: log is shortcut for log.log, we can disable output.

log ==== log.log
  .{...console API}
  .enable() -> void
  .disable() -> void

// Before:
if(window.console && console.warn)console.warn(42);
// After:
log.warn(42);

// Before:
setTimeout(console.warn.bind(console, 42), 1000);
[1, 2, 3].forEach(console.warn, console);
// After:
setTimeout(log.warn, 1000, 42);
[1, 2, 3].forEach(log.warn);

// log is shortcut for log.log
setImmediate(log, 42); // => 42

log.disable();
log.warn('Console is disabled, you will not see this message.');
log.enable();
log.warn('Console is enabled again.');

Missing polyfills

• ES5 JSON is missing now only in IE7- and never it will be added to core-js, if you need it in these old browsers available many implementations, for example, json3.
• ES6 Typed Arrays can be polyfilled without serious problems, but it will be slow - getter / setter for each element and they are missing completely only in IE9-. You can use this polyfill. Possible, it will be added to core-js in the future, completely or only missing methods of existing arrays.
• ES6 String#normalize is not very usefull feature, but this polyfill will be very large. If you need it, you can use unorm.
• ES6 Proxy can't be polyfilled, but for Node.js / Chromium with additional flags you can try harmony-reflect for adapt old style Proxy API to final ES6 version.
• ES6 logic for @@isConcatSpreadable and @@species (in most places) can be polyfilled without problems, but it will cause serious slowdown in popular cases in some engines. It will be polyfilled when it will be implemented in modern engines.
• ES7 Object.observe can be polyfilled with many limitations, but it will be very slow - dirty checking on each tick. In nearest future it will not be added to core-js - it will cause serious slowdown in applications which uses Object.observe and fallback if it's missing. Possible it will be added as optional feature then most actual browsers will have this feature. Now you can use this polyfill.
• ES7 SIMD. core-js doesn't adds polyfill of this feature because of large size and some other reasons. You can use this polyfill.
• window.fetch is not crossplatform feature, in some environments it make no sense. For this reason I don't think it should be in core-js. Looking at the large number of requests it maybe added in the future. Now you can use, for example, this polyfill.