The core-js npm package is a modular standard library for JavaScript, which includes polyfills for ECMAScript features. It provides reliable polyfills to ensure that code behaves consistently across different environments, including older browsers.
Polyfilling ECMAScript features
This feature allows developers to use the latest ECMAScript features while ensuring backward compatibility with older environments that do not support these features natively.
require('core-js/stable');
// Now you can use ES6 features like Promise in environments that do not support them natively.Polyfilling Web Standards
Core-js can also polyfill web standards, allowing developers to use modern web APIs in environments that have not implemented them.
require('core-js/web');
// This includes polyfills for web standards like DOM collections (e.g., NodeList), timers, and more.Polyfilling Proposals
Developers can experiment with proposed ECMAScript features before they are finalized and adopted into the standard, ensuring forward compatibility.
require('core-js/proposals');
// This will include polyfills for ECMAScript proposals that are not yet part of the standard.Babel-polyfill is a package that provides polyfills necessary for a full ES2015+ environment. It is similar to core-js but is more tightly coupled with Babel's transpilation process.
The es6-shim package provides polyfills for ECMAScript 6 (aka ECMAScript 2015) features. It is similar to core-js but focuses specifically on ES6 features and does not cover proposals or web standards.
The polyfill-service by Financial Times is an online service that provides polyfills based on the user's browser. It is different from core-js in that it is a service rather than a package you include in your project, but it serves a similar purpose in polyfilling features.
Alternative modular compact (max. ~23kb w/o gzip) standard library for JavaScript. Includes polyfills for ECMAScript 5, ECMAScript 6: symbols, collections, iterators, promises; setImmediate, array generics, console cap. Some additional functionality such as dictionaries, extended partial application, date formatting.
console.log(Array.from(new Set([1, 2, 3, 2, 1]))); // => [1, 2, 3]
console.log('*'.repeat(10)); // => '**********'
Promise.resolve(32).then(console.log); // => 32
setImmediate(console.log, 42); // => 42
Without extension of native objects:
var log = core.console.log;
log(core.Array.from(new core.Set([1, 2, 3, 2, 1]))); // => [1, 2, 3]
log(core.String.repeat('*', 10)); // => '**********'
core.Promise.resolve(32).then(log); // => 32
core.setImmediate(log, 42); // => 42
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
.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-
.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)
String
#trim() -> str
Date
.now() -> int
Module es6. About iterators from this module here. Symbols, collections and promises in separate modules.
Object
.assign(target, ...src) -> target
.is(a, b) -> bool
.setPrototypeOf(target, proto | null) -> target, sham(ie11+)
#toString() -> string, fix for @@toStringTag support
Function
#name -> string (IE9+)
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]'
(function foo(){}).name // => 'foo'
Array
.from(iterable | array-like, mapFn(val, index)?, that) -> array
.of(...args) -> array
#copyWithin(target = 0, start = 0, end = @length) -> @
#fill(var, start = 0, end = @length) -> @
#find(fn(val, index, @), that) -> var
#findIndex(fn(val, index, @), that) -> int
#@@unscopables -> object
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]
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
RegExp
#flags -> str (getter, IE9+)
'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!'
String.raw({raw: 'test'}, 0, 1, 2); // => 't0e1s2t'
/foo/.flags; // => ''
/foo/gim.flags; // => 'gim'
Number
.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
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 (IE10+)
.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
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
.pure(description?) -> symbol || string
.set(object, key, val) -> object
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'
By default, Symbol polyfill define setter in Object.prototype. You can disable it. 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
Reflect.ownKeys from Reflect module returns all object keys - strings & symbols.
Module es6_collections. 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
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]]
new Set(iterable?) -> set
#add(key) -> @
#clear() -> void
#delete(key) -> bool
#forEach(fn(el, el, @), that) -> void
#has(key) -> bool
#size
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']
new WeakMap(iterable (entries) ?) -> weakmap
#delete(key) -> bool
#get(key) -> val
#has(key) -> bool
#set(key, val) -> @
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'
new WeakSet(iterable?) -> weakset
#add(key) -> @
#delete(key) -> bool
#has(key) -> bool
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
Module es6:
String
#@@iterator() -> iterator
Array
#values() -> iterator
#keys() -> iterator
#entries() -> iterator (entries)
#@@iterator() -> iterator
Arguments
#@@iterator() -> iterator (sham, available only in core-js methods)
Module es6_collections:
Set
#values() -> iterator
#keys() -> iterator
#entries() -> iterator (entries)
#@@iterator() -> iterator
Map
#values() -> iterator
#keys() -> iterator
#entries() -> iterator (entries)
#@@iterator() -> iterator (entries)
var string = 'a𠮷b';
for(var val of string)console.log(val); // => 'a', '𠮷', 'b'
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'
}
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
}
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 $for - iterators chaining - for-of and array / generator comprehensions helpers for ES5- syntax.
$for(iterable, entries) -> iterator ($for)
#of(fn(value, key?), that) -> void
#array(mapFn(value, key?)?, that) -> array
#filter(fn(value, key?), that) -> iterator ($for)
#map(fn(value, key?), that) -> iterator ($for)
.isIterable(var) -> bool
.getIterator(iterable) -> iterator
$for(new Set([1, 2, 3, 2, 1])).of(function(it){
console.log(it); // => 1, 2, 3
});
$for([1, 2, 3].entries(), true).of(function(key, value){
console.log(key); // => 0, 1, 2
console.log(value); // => 1, 2, 3
});
$for('abc').of(console.log, console); // => 'a', 'b', 'c'
$for([1, 2, 3, 4, 5]).of(function(it){
console.log(it); // => 1, 2, 3
if(it == 3)return false;
});
var ar1 = $for([1, 2, 3]).array(function(v){
return v * v;
}); // => [1, 4, 9]
var set = new Set([1, 2, 3, 2, 1]);
var ar1 = $for(set).filter(function(v){
return v % 2;
}).array(function(v){
return v * v;
}); // => [1, 9]
var iter = $for(set).filter(function(v){
return v % 2;
}).map(function(v){
return v * v;
});
iter.next(); // => {value: 1, done: false}
iter.next(); // => {value: 9, done: false}
iter.next(); // => {value: undefined, done: true}
var map1 = new Map([['a', 1], ['b', 2], ['c', 3]]);
var map2 = new Map($for(map1, true).filter(function(k, v){
return v % 2;
}).map(function(k, v){
return [k + k, v * v];
})); // => Map {aa: 1, cc: 9}
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:
var log = console.log.bind(console);
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.
}
})();
Module es6_reflect.
Reflect
.apply(target, thisArgument, argumentsList) -> var
.construct(target, argumentsList) -> 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, sham(ie11+)
var O = {a: 1};
Object.defineProperty(O, 'b', {value: 2});
O[Symbol('c')] = 3;
console.log(Reflect.ownKeys(O)); // => ['a', 'b', Symbol(c)]
function C(a, b){
this.c = a + b;
}
var instance = Reflect.construct(C, [20, 22]);
console.log(instance.c); // => 42
Module es7.
Array#includes proposalString#at proposalObject.values, Object.entries tc39 discussRegExp.escape proposalArray
#includes(var, from?) -> bool
String
#at(index) -> string
Object
.values(object) -> array
.entries(object) -> array
RegExp
.escape(str) -> str
[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
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]]
RegExp.escape('Hello -[]{}()*+?.,\\^$|'); // => 'Hello \-\[\]\{\}\(\)\*\+\?\.\,\\\^\$\|'
Module es7_refs. Symbols and methods for abstract references. At the moment, they are supported only by several translators, such as 6to5.
Symbol
.referenceGet -> @@referenceGet
.referenceSet -> @@referenceSet
.referenceDelete -> @@referenceDelete
Function
#@@referenceGet() -> @
Map
#@@referenceGet ==== #get
#@@referenceSet ==== #set
#@@referenceDelete ==== #delete
WeakMap
#@@referenceGet ==== #get
#@@referenceSet ==== #set
#@@referenceDelete ==== #delete
Private properties example with WeakMaps, class and basic abstract refs syntax:
var Person = (NAME => class {
constructor(name){
this::NAME = name;
}
getName(){
return this::NAME;
}
})(new WeakMap);
var person = new Person('Vasya');
console.log(person.getName()); // => 'Vasya'
for(var key in person)console.log(key); // => only 'getName'
The same example with the private keyword:
class Person {
private NAME
constructor(name){
this::NAME = name;
}
getName(){
return this::NAME;
}
}
var person = new Person('Vasya');
console.log(person.getName()); // => 'Vasya'
for(var key in person)console.log(key); // => only 'getName'
Virtual methods example:
var {toString} = {};
[]::toString() // => '[object Array]'
function sum(){
var {reduce} = [];
return arguments::reduce((a, b)=> a + b);
}
sum(1, 2, 3, 4, 5) // => 15
Virtual size property for dictionaries example:
let size = {
[Symbol.referenceGet](it){
return Object.keys(it).length;
},
[Symbol.referenceSet](it, length){
for(let key of Object.keys(it).slice(length))delete it[key];
}
}
{q: 1, w: 2, e: 3}::size // => 3
var dict = {q: 1, w: 2, e: 3};
dict::size = 2;
dict // => {q: 1, w: 2};
Methods from Dict module override @@referenceGet method, example:
var {filter, map} = Dict;
var dict = {q: 1, w: 2, e: 3}
::filter((v, k) => k != 'w')
::map(v => v * v); // => {"q":1,"e":9}
Module 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'}
Module 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);
Module immediate. setImmediate polyfill.
setImmediate(fn(...args), ...args) -> id
clearImmediate(id) -> void
setImmediate(function(arg1, arg2){
console.log(arg1, arg2); // => Message will be displayed with minimum delay
}, 'Message will be displayed', 'with minimum delay');
clearImmediate(setImmediate(function(){
console.log('Message will not be displayed');
}));
Module console. Console cap for old browsers and some additional functionality.
console
.{...console API}
.enable() -> void
.disable() -> void
// Before:
if(window.console && console.log)console.log(42);
// After:
console.log(42);
// Before:
setTimeout(console.log.bind(console, 42), 1000);
[1, 2, 3].forEach(console.log, console);
// After:
setTimeout(console.log, 1000, 42);
[1, 2, 3].forEach(console.log);
console.disable();
console.warn('Console is disabled, you will not see this message.');
console.enable();
console.warn('Console is enabled again.');
Module object.
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);
console.log(vector.xy); // => 15
console.log(vector.xyz); // => 25
vector.y++;
console.log(vector.xy); // => 15.811388300841896
console.log(vector.xyz); // => 25.495097567963924
Module dict. Based on TC39 discuss / strawman.
[new] Dict(itarable (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
.turn(object, fn(memo, val, key, @), memo = new @) -> memo
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 return iterators for objects, examples:
var dict = {a: 1, b: 2, c: 3};
for(var key of Dict.keys(dict))console.log(key); // => 'a', 'b', 'c'
for(var [key, val] of Dict.entries(dict)){
console.log(key); // => 'a', 'b', 'c'
console.log(val); // => 1, 2, 3
}
$for(Dict.values(dict)).of(console.log); // => 1, 2, 3
new Map(Dict.entries(dict)); // => Map {a: 1, b: 2, c: 3}
new Map((for([k, v] of Dict.entries(dict))if(v % 2)[k + k, v * v])); // => Map {aa: 1, cc: 9}
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'
Dict.turn(dict, function(memo, it, key){
memo[key + key] = it;
}); // => {aa: 1, bb: 2, cc: 3}
Dict.turn(dict, function(memo, it, key){
it % 2 && memo.push(key + it);
}, []); // => ['a1', 'c3']
Module binding.
Function
#part(...args | _) -> fn(...args)
#by(object | _, ...args | _) -> boundFn(...args)
#only(num, that /* = @ */) -> (fn | boundFn)(...args)
Object
#[_](key) -> boundFn
Function#part partial apply function without this binding. Uses global variable _ (core._ for builds without extension of native objects) as placeholder. Examples:
var fn1 = console.log.part(1, 2);
fn1(3, 4); // => 1, 2, 3, 4
var fn2 = console.log.part(_, 2, _, 4);
fn2(1, 3); // => 1, 2, 3, 4
var fn3 = console.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
Method Function#by is analogue of Function#bind with the ability to use placeholder:
var fn = console.log.by(console, _, 2, _, 4);
fn(1, 3, 5); // => 1, 2, 3, 4, 5
Method Object#[_] extracts bound method from object, examples:
['foobar', 'foobaz', 'barbaz'].filter(/bar/[_]('test')); // => ['foobar', 'barbaz']
var has = {}.hasOwnProperty[_]('call');
log(has({key: 42}, 'foo')); // => false
log(has({key: 42}, 'key')); // => true
var array = []
, push = array[_]('push');
push(1);
push(2, 3);
log(array); // => [1, 2, 3];
Method Function#only limits number of arguments. Example:
[1, 2, 3].forEach(log.only(1)); // => 1, 2, 3
Module date. Much more simple and compact (~60 lines with en & ru locales) than Intl or Moment.js. Use them if you need extended work with Date.
Date
#format(str, key?) -> str
#formatUTC(str, key?) -> str
core
.addLocale(key, object) -> core
.locale(key?) -> key
| Token | Unit | Sample |
|---|---|---|
| s | Seconds | 0-59 |
| ss | Seconds, 2 digits | 00-59 |
| m | Minutes | 0-59 |
| mm | Minutes, 2 digits | 00-59 |
| h | Hours | 0-23 |
| hh | Hours, 2 digits | 00-23 |
| D | Date | 1-31 |
| DD | Date, 2 digits | 01-31 |
| W | Weekday, string | Вторник |
| N | Month | 1-12 |
| NN | Month, 2 digits | 01-12 |
| M | Month, string | Ноябрь |
| MM | Of month, string | Ноября |
| Y | Year, full | 2014 |
| YY | Year, 2 digits | 14 |
| Examples: |
new Date().format('W, MM D, YY, h:mm:ss'); // => 'Friday, November 28, 14, 18:47:05'
new Date().formatUTC('W, MM D, YY, h:mm:ss'); // => 'Friday, November 28, 14, 12:47:05'
new Date().format('W, D MM Y г., h:mm:ss', 'ru'); // => 'Пятница, 28 Ноября 2014 г., 18:07:25'
core.locale('ru');
new Date().format('W, D MM Y г., h:mm:ss'); // => 'Пятница, 28 Ноября 2014 г., 18:07:25'
new Date().format('DD.NN.YY'); // => '28.11.14'
new Date().format('hh:mm:ss'); // => '18:47:05'
new Date().format('DD.NN.Y hh:mm:ss'); // => '28.11.2014 18:47:05'
new Date().format('W, D MM Y года'); // => 'Пятница, 28 Ноября 2014 года'
new Date().format('D MM, h:mm'); // => '28 Ноября, 16:47'
new Date().format('M Y'); // => 'Ноябрь 2014'
(typeof core != 'undefined' ? core : require('core-js/library')).addLocale('ru', {
weekdays: 'Воскресенье,Понедельник,Вторник,Среда,Четверг,Пятница,Суббота',
months: 'Январ:я|ь,Феврал:я|ь,Март:а|,Апрел:я|ь,Ма:я|й,Июн:я|ь,Июл:я|ь,Август:а|,Сентябр:я|ь,Октябр:я|ь,Ноябр:я|ь,Декабр:я|ь'
});
Module array.
Array
#turn(fn(memo, val, index, @), memo = []) -> memo
Method Array#turn reduce array to object, example:
[1, 2, 3, 4, 5].turn(function(memo, it){
memo['key' + it] = !!(it % 2);
}, {}); // => {key1: true, key2: false, key3: true, key4: false, key5: true}
[1, 2, 3, 4, 5, 6, 7, 8, 9].turn(function(memo, it){
it % 2 && memo.push(it * it);
if(memo.length == 3)return false;
}); // => [1, 9, 25]
Module number.
Number
#@@iterator() -> iterator
#random(lim = 0) -> num
#{...Math}
Number Iterator examples:
for(var i of 3)console.log(i); // => 0, 1, 2
$for(3).of(console.log); // => 0, 1, 2
Array.from(10, Math.random); // => [0.9817775336559862, 0.02720663254149258, ...]
Array.from(10); // => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
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]
// Comprehensions:
[for(i of 10)if(i % 2)i * i]; // => [1, 9, 25, 49, 81]
Dict((for(i of 3)['key' + i, !(i % 2)])); // => {key0: true, key1: false, key2: true}
$for(10).filter(function(i){
return i % 2;
}).array(function(i){
return i * i;
}); // => [1, 9, 25, 49, 81]
Dict($for(3).map(function(i){
return ['key' + i, !(i % 2)];
})); // => {key0: true, key1: false, key2: true}
Math methods in Number.prototype examples:
3..pow(3); // => 27
(-729).abs().sqrt(); // => 27
10..random(20); // => Random number (10, 20), for example, 16.818793776910752
10..random(20).floor(); // => Random integer [10, 19], for example, 16
var array = [1, 2, 3, 4, 5];
array[array.length.random().floor()]; // => Random element, for example, 4
Module string.
String
#escapeHTML() -> str
#unescapeHTML() -> str
'<script>doSomething();</script>'.escapeHTML(); // => '<script>doSomething();</script>'
'<script>doSomething();</script>'.unescapeHTML(); // => '<script>doSomething();</script>'
// Node.js:
npm i core-js
// Bower:
bower install core.js
Browser builds: default, without extension of native objects, shim only.
Custom builds:
npm i -g grunt-cli
npm i core-js
cd node_modules/core-js && npm i
grunt build:date,console,library --path=custom uglify
Where date and console are module names, library is flag for not extension of native objects and custom is target file name.
Require in Node.js:
// Dafault
require('core-js');
// Without extension of native objects
var core = require('core-js/library');
// Shim only
require('core-js/shim');
0.4.5 - 2015.01.16 - Some fixes
0.4.4 - 2015.01.11 - Enabled CSP support
0.4.3 - 2015.01.10 - Added Function instances name property for IE9+
0.4.2 - 2015.01.10
Object static methods accept primitivesRegExp constructor can alter flags (IE9+)Array.prototype[Symbol.unscopables]0.4.1 - 2015.01.05 - Some fixes
0.4.0 - 2015.01.03
es6_reflect module:
Reflect.applyReflect.constructReflect.definePropertyReflect.deletePropertyReflect.enumerateReflect.getReflect.getOwnPropertyDescriptorReflect.getPrototypeOfReflect.hasReflect.isExtensibleReflect.preventExtensionsReflect.setReflect.setPrototypeOfSymbol.iterator polyfill0.3.3 - 2014.12.28
0.3.2 - 2014.12.25
console bug0.3.1 - 2014.12.23 - Some fixes
0.3.0 - 2014.12.23 - Optimize Map & Set
es6 and es6_collections modules0.2.5 - 2014.12.20
console no longer shortcut for console.log (compatibility problems)0.2.4 - 2014.12.17 - Better compliance of ES6
Math.fround (IE10+)0.2.3 - 2014.12.15 - Symbols:
Object.prototype for Symbol polyfill:
Symbol.useSimpleSymbol.useSetterSymbol.hasInstanceSymbol.isConcatSpreadableSymbol.matchSymbol.replaceSymbol.searchSymbol.speciesSymbol.splitSymbol.toPrimitiveSymbol.unscopables0.2.2 - 2014.12.13 - ES6:
RegExp#flags (December 2014 Draft Rev 29)String.raw0.2.1 - 2014.12.12 - Repair converting -0 to +0 in native collections
0.2.0 - 2014.12.06
es7, es7_refs modulesString#atSymbol.referenceGetSymbol.referenceSetSymbol.referenceDeleteFunction#@@referenceGetMap#@@referenceGetMap#@@referenceSetMap#@@referenceDeleteWeakMap#@@referenceGetWeakMap#@@referenceSetWeakMap#@@referenceDeleteDict.{...methods}[@@referenceGet].contains methods0.1.5 - 2014.12.01 - ES6:
Array#copyWithinString#codePointAtString.fromCodePoint0.1.4 - 2014.11.27
Dict.mapPairs0.1.3 - 2014.11.20 - TC39 November meeting:
.contains -> .includes
String#contains -> String#includesArray#contains -> Array#includesDict.contains -> Dict.includesWeakMap#clearWeakSet#clear0.1.2 - 2014.11.19 - Map & Set bug fix
0.1.1 - 2014.11.18 - Public release
FAQs
Standard library
The npm package core-js receives a total of 29,062,431 weekly downloads. As such, core-js popularity was classified as popular.
We found that core-js demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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