Core JS

https://github.com/zloirock/core-js
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Core JS is a modular standard library for JavaScript, providing polyfills for ECMAScript features up...
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### Prepare Monorepo and Install Dependencies

Source: https://github.com/zloirock/core-js/blob/master/CONTRIBUTING.md

Run this command to set up the monorepo and install all necessary dependencies before testing.

```sh
npm run prepare-monorepo
```

--------------------------------

### WeakMap Usage Example

Source: https://github.com/zloirock/core-js/blob/master/README.md

Demonstrates basic WeakMap operations like setting, getting, checking for keys, and deleting entries. Also shows how to use WeakMap for private properties.

```javascript
let a = [1];
let b = [2];
let c = [3];

let weakmap = new WeakMap([[a, 1], [b, 2]]);
weakmap.set(c, 3).set(b, 4);
console.log(weakmap.has(a));   // => true
console.log(weakmap.has([1])); // => false
console.log(weakmap.get(a));   // => 1
weakmap.delete(a);
console.log(weakmap.get(a));   // => undefined

// Private properties store:
let Person = (() => {
  let names = new WeakMap();
  return class {
    constructor(name) {
      names.set(this, name);
    }
    getName() {
      return names.get(this);
    }
  };
})();

let person = new Person('Vasya');
console.log(person.getName());            // => 'Vasya'
for (let key in person) console.log(key); // => only 'getName'
```

--------------------------------

### core-js Examples in Deno

Source: https://github.com/zloirock/core-js/blob/master/deno/corejs/README.md

Demonstrates the usage of various core-js features within a Deno environment after importing the library. Includes examples for Object.hasOwn, Array.prototype.at, Array.prototype.group, Promise.any, and iterator helpers.

```javascript
Object.hasOwn({ foo: 42 }, 'foo');   // => true

[1, 2, 3, 4, 5, 6, 7].at(-3);        // => 5

[1, 2, 3, 4, 5].group(it => it % 2); // => { 1: [1, 3, 5], 0: [2, 4] }

Promise.any([
  Promise.resolve(1),
  Promise.reject(2),
  Promise.resolve(3),
]).then(console.log);                // => 1

(function * (i) { while (true) yield i++; })(1)
  .drop(1).take(5)
  .filter(it => it % 2)
  .map(it => it ** 2)
  .toArray();                        // => [9, 25]
```

--------------------------------

### Map Usage Examples

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/collections.md

Demonstrates common Map operations including initialization, setting and getting values, checking for keys, iteration, and deletion. Also shows the use of `Map.groupBy` for grouping elements.

```javascript
let array = [1];

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

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

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

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

map = Map.groupBy([1, 2, 3, 4, 5], it => it % 2);
map.get(1); // => [1, 3, 5]
map.get(0); // => [2, 4]


map = new Map([['a', 1]]);

map.getOrInsert('a', 2); // => 1

map.getOrInsert('b', 3); // => 3

map.getOrInsertComputed('a', key => key); // => 1

map.getOrInsertComputed('c', key => key); // => 'c'

console.log(map); // => Map { 'a': 1, 'b': 3, 'c': 'c' }
```

--------------------------------

### Map Basic Usage Example

Source: https://github.com/zloirock/core-js/blob/master/README.md

Demonstrates fundamental Map operations including setting, getting, checking for keys, deleting, and iterating over entries. Shows how Map handles different key types.

```javascript
let array = [1];

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

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

--------------------------------

### Install core-js Versions

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/usage.md

Install core-js using npm. Choose between the global, pure (no global pollution), or bundled versions.

```sh
// global version
npm install --save core-js@3.49.0
// version without global namespace pollution
npm install --save core-js-pure@3.49.0
// bundled global version
npm install --save core-js-bundle@3.49.0
```

--------------------------------

### Basic Observable Usage Example

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/observable.md

Demonstrates how to create and subscribe to an Observable, emitting values and completing.

```javascript
new Observable(observer => {
  observer.next('hello');
  observer.next('world');
  observer.complete();
}).subscribe({
  next(it) { console.log(it); },
  complete() { console.log('!'); },
});
```

--------------------------------

### Promise All Example

Source: https://github.com/zloirock/core-js/blob/master/README.md

Demonstrates `Promise.all` for running multiple promises concurrently and waiting for all to complete.

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

--------------------------------

### Set.of Example

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/of-and-from-methods-on-collections.md

Demonstrates the usage of the Set.of static method to create a new Set with unique values from provided arguments.

```javascript
Set.of(1, 2, 3, 2, 1); // => Set {1, 2, 3}
```

--------------------------------

### String PadStart and PadEnd Methods

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/string-regexp.md

Demonstrates padding a string with another string until it reaches a specified length, either at the start or end.

```javascript
'hello'.padStart(10);         // => '     hello'
'hello'.padStart(10, '1234'); // => '12341hello'
'hello'.padEnd(10);           // => 'hello     '
'hello'.padEnd(10, '1234'); // => 'hello12341'
```

--------------------------------

### Install core-js and regenerator-runtime dependencies

Source: https://github.com/zloirock/core-js/blob/master/docs/2019-03-19-core-js-3-babel-and-a-look-into-the-future.md

Install the necessary core-js and regenerator-runtime packages as direct dependencies for your project.

```bash
npm i --save core-js regenerator-runtime
```

--------------------------------

### core-js-compat Targets Option Examples

Source: https://github.com/zloirock/core-js/blob/master/packages/core-js-compat/README.md

Demonstrates how to specify browser targets using either a browserslist query string or a detailed targets object.

```javascript
// browserslist query:
'defaults, not IE 11, maintained node versions';
```

```javascript
// object (sure, all those fields optional):
({
  android: '4.0',         // Android WebView version
  bun: '0.1.2',           // Bun version
  chrome: '38',           // Chrome version
  'chrome-android': '18', // Chrome for Android version
  deno: '1.12',           // Deno version
  edge: '13',             // Edge version
  electron: '5.0',        // Electron framework version
  firefox: '15',          // Firefox version
  'firefox-android': '4', // Firefox for Android version
  hermes: '0.11',         // Hermes version
  ie: '8',                // Internet Explorer version
  ios: '13.0',            // iOS Safari version
  node: 'current',        // NodeJS version, you can use 'current' for set it to currently used
  opera: '12',            // Opera version
  'opera-android': '7',   // Opera for Android version
  phantom: '1.9',         // PhantomJS headless browser version
  quest: '5.0',           // Meta Quest Browser version
  'react-native': '0.70', // React Native version (default Hermes engine)
  rhino: '1.7.13',        // Rhino engine version
  safari: '14.0',         // Safari version
  samsung: '14.0',        // Samsung Internet version
  /**
   * true option set target to minimum supporting ES Modules versions of all browsers, ignoring `browsers` target.
   * 'intersect' option intersects the `browsers` target and `browserslist`'s targets. The maximum version will be used.
   */
  esmodules: true | 'intersect',
  browsers: '> 0.25%',    // Browserslist query or object with target browsers
});
```

--------------------------------

### Promise Resolve and Reject Example

Source: https://github.com/zloirock/core-js/blob/master/README.md

Illustrates how to use `Promise.resolve` and `Promise.reject` to create already settled promises.

```javascript
/* eslint-disable promise/prefer-await-to-callbacks -- example */
Promise.resolve(42).then(x => console.log(x));         // => 42
Promise.reject(42).catch(error => console.log(error)); // => 42

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

--------------------------------

### Math.sumPrecise Example

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/math.md

Demonstrates the usage of Math.sumPrecise to achieve precise summation of numbers.

```APIDOC
## Examples

### Precise Summation

```js
// Standard floating-point addition can lead to inaccuracies
1e20 + 0.1 + -1e20; // => 0

// Math.sumPrecise provides a more accurate result
Math.sumPrecise([1e20, 0.1, -1e20]); // => 0.1
```
```

--------------------------------

### Full core-js Import Example

Source: https://github.com/zloirock/core-js/blob/master/packages/core-js/README.md

Demonstrates the usage of various core-js features with a full import. This method pollutes the global namespace.

```javascript
import 'core-js/actual';

Promise.try(() => 42).then(it => console.log(it)); // => 42

Array.from(new Set([1, 2, 3]).union(new Set([3, 4, 5]))); // => [1, 2, 3, 4, 5]

[1, 2].flatMap(it => [it, it]); // => [1, 1, 2, 2]

Iterator.concat([1, 2], function * (i) { while (true) yield i++; }(3))
  .drop(1).take(5)
  .filter(it => it % 2)
  .map(it => it ** 2)
  .toArray(); // => [9, 25]

structuredClone(new Set([1, 2, 3])); // => new Set([1, 2, 3])
```

--------------------------------

### Using console.log for Output

Source: https://github.com/zloirock/core-js/blob/master/website/src/playground.html

Demonstrates how to use console.log() to display output from core-js examples. This is a standard method for debugging and observing results.

```javascript
console.log()
```

--------------------------------

### Map Upsert Examples

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/map-upsert.md

Demonstrates the usage of `getOrInsert` and `getOrInsertComputed` methods on a `Map` object. Shows how to insert or retrieve existing values.

```javascript
const map = new Map([['a', 1]]);

map.getOrInsert('a', 2); // => 1

map.getOrInsert('b', 3); // => 3

map.getOrInsertComputed('a', key => key); // => 1

map.getOrInsertComputed('c', key => key); // => 'c'

console.log(map); // => Map { 'a': 1, 'b': 3, 'c': 'c' }
```

--------------------------------

### Using Reflect.defineMetadata and Reflect.getOwnMetadata

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/reflect-metadata.md

Demonstrates how to define and retrieve metadata on an object using Reflect.defineMetadata and Reflect.getOwnMetadata. This example shows that ownKeys does not include metadata keys.

```javascript
let object = {};
Reflect.defineMetadata('foo', 'bar', object);
Reflect.ownKeys(object);               // => []
Reflect.getOwnMetadataKeys(object);    // => ['foo']
Reflect.getOwnMetadata('foo', object); // => 'bar'
```

--------------------------------

### core-js-compat Full Modules List

Source: https://github.com/zloirock/core-js/blob/master/packages/core-js-compat/README.md

Shows how to get a flat array containing all available module names within core-js.

```javascript
// full list of modules:
require('core-js-compat/modules'); // => Array<ModuleName>
```

```javascript
// or
require('core-js-compat').modules; // => Array<ModuleName>
```

--------------------------------

### Math.sumPrecise Example

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/math.md

Demonstrates the usage of Math.sumPrecise for accurate summation of numbers, contrasting with standard addition which can lose precision.

```javascript
1e20 + 0.1 + -1e20; // => 0
Math.sumPrecise([1e20, 0.1, -1e20]); // => 0.1
```

--------------------------------

### Import core-js for Deno

Source: https://github.com/zloirock/core-js/blob/master/deno/corejs/README.md

Import the core-js library at the top of your Deno entry point to enable polyfills. This example uses a specific version of core-js.

```javascript
import 'https://deno.land/x/corejs@v3.49.0/index.js';
```

--------------------------------

### Iterator Chunking and Windowing Examples

Source: https://github.com/zloirock/core-js/blob/master/README.md

Demonstrates the usage of Iterator.chunks and Iterator.windows with different parameters. Shows how to create chunks and sliding windows, including handling undersized windows.

```javascript
const digits = () => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9].values();

let chunks = Array.from(digits().chunks(2));  // [[0, 1], [2, 3], [4, 5], [6, 7], [8, 9]]

let windows = Array.from(digits().windows(2));  // [[0, 1], [1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 7], [7, 8], [8, 9]]

let windowsPartial = Array.from([0, 1].values().windows(3, 'allow-partial'));  // [[0, 1]]

let windowsFull = Array.from([0, 1].values().windows(3));  // []
```

--------------------------------

### core-js-compat compat() Method

Source: https://github.com/zloirock/core-js/blob/master/packages/core-js-compat/README.md

Shows how to use the `compat()` method to get a list of required core-js modules for specified targets and optionally filter by modules and version.

```javascript
// equals of of the method from the example above
require('core-js-compat/compat')({ targets, modules, version }); // => { list: Array<ModuleName>, targets: { [ModuleName]: { [EngineName]: EngineVersion } } }
```

```javascript
// or
require('core-js-compat').compat({ targets, modules, version }); // => { list: Array<ModuleName>, targets: { [ModuleName]: { [EngineName]: EngineVersion } } }
```

--------------------------------

### SWC Configuration for Core-JS

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/usage.md

Example of configuring SWC's environment settings, including target browsers, mode, and core-js version, within a `.swcrc` file.

```json
{
  "env": {
    "targets": "> 0.25%, not dead",
    "mode": "entry",
    "coreJs": "3.49"
  }
}
```

--------------------------------

### Reflect.construct Example

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/reflect.md

Shows how Reflect.construct() is used to invoke a constructor with arguments, creating a new instance.

```javascript
function C(a, b) {
  this.c = a + b;
}

let instance = Reflect.construct(C, [20, 22]);
instance.c; // => 42
```

--------------------------------

### Joint Iteration Examples

Source: https://github.com/zloirock/core-js/blob/master/README.md

Demonstrates the usage of Iterator.zip and Iterator.zipKeyed with different modes and padding options. Shows how to iterate over multiple iterables concurrently.

```javascript
Iterator.zip([
  [0, 1, 2],
  [3, 4, 5],
]).toArray();  // => [[0, 3], [1, 4], [2, 5]]

Iterator.zipKeyed({
  a: [0, 1, 2],
  b: [3, 4, 5, 6],
  c: [7, 8, 9],
}, {
  mode: 'longest',
  padding: { c: 10 },
}).toArray();
/*
[
  { a: 0,         b: 3, c: 7  },
  { a: 1,         b: 4, c: 8  },
  { a: 2,         b: 5, c: 9  },
  { a: undefined, b: 6, c: 10 },
];
 */
```

--------------------------------

### String Includes, StartsWith, and EndsWith Methods

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/string-regexp.md

Shows how to check for the presence of substrings, their starting positions, and ending positions within a string.

```javascript
'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
```

--------------------------------

### Pure core-js Import Example (No Global Pollution)

Source: https://github.com/zloirock/core-js/blob/master/packages/core-js/README.md

Demonstrates importing core-js features without polluting the global namespace, using named imports from 'core-js-pure'.

```javascript
import Promise from 'core-js-pure/actual/promise';
import Set from 'core-js-pure/actual/set';
import Iterator from 'core-js-pure/actual/iterator';
import from from 'core-js-pure/actual/array/from';
import flatMap from 'core-js-pure/actual/array/flat-map';
import structuredClone from 'core-js-pure/actual/structured-clone';

Promise.try(() => 42).then(it => console.log(it)); // => 42

from(new Set([1, 2, 3]).union(new Set([3, 4, 5]))); // => [1, 2, 3, 4, 5]

flatMap([1, 2], it => [it, it]); // => [1, 1, 2, 2]

Iterator.concat([1, 2], function * (i) { while (true) yield i++; }(3))
  .drop(1).take(5)
  .filter(it => it % 2)
  .map(it => it ** 2)
  .toArray(); // => [9, 25]

structuredClone(new Set([1, 2, 3])); // => new Set([1, 2, 3])
```

--------------------------------

### Promise.withResolvers Example

Source: https://github.com/zloirock/core-js/blob/master/README.md

Shows how to use `Promise.withResolvers` to create a promise with explicit resolve and reject methods. The promise is resolved with a value, and the result is logged.

```javascript
const d = Promise.withResolvers();
d.resolve(42);
d.promise.then(console.log); // => 42
```

--------------------------------

### Using Iteration Helpers with Arguments Object

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/iteration-helpers.md

Demonstrates how to use isIterable, getIterator, and getIteratorMethod with the arguments object. Ensure the 'actual' path is imported for these examples.

```javascript
import isIterable from 'core-js-pure/actual/is-iterable';
import getIterator from 'core-js-pure/actual/get-iterator';
import getIteratorMethod from 'core-js-pure/actual/get-iterator-method';

let list = (function () {
  // eslint-disable-next-line prefer-rest-params -- example
  return arguments;
})(1, 2, 3);

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

let iterator = getIterator(list);
console.log(iterator.next().value); // 1
console.log(iterator.next().value); // 2
console.log(iterator.next().value); // 3
console.log(iterator.next().value); // undefined

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

let method = getIteratorMethod(list);
console.log(typeof method);         // 'function'
iterator = method.call(list);
console.log(iterator.next().value); // 1
console.log(iterator.next().value); // 2
console.log(iterator.next().value); // 3
console.log(iterator.next().value); // undefined

console.log(getIteratorMethod({})); // undefined
```

--------------------------------

### Babel Preset Env: 'usage' mode example

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/usage.md

With `useBuiltIns: 'usage'`, polyfills for features used in a file and not supported by the target environment are automatically imported at the top of the file.

```typescript
// first file:
let set = new Set([1, 2, 3]);
```

```typescript
// second file:
let array = Array.of(1, 2, 3);
```

```typescript
// first file:
import 'core-js/modules/es.array.iterator';
import 'core-js/modules/es.object.to-string';
import 'core-js/modules/es.set';

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

```typescript
// second file:
import 'core-js/modules/es.array.of';

var array = Array.of(1, 2, 3);
```

--------------------------------

### Selective core-js Import Example

Source: https://github.com/zloirock/core-js/blob/master/packages/core-js/README.md

Shows how to import specific features from core-js to reduce bundle size. This method also pollutes the global namespace.

```javascript
import 'core-js/actual/promise';
import 'core-js/actual/set';
import 'core-js/actual/iterator';
import 'core-js/actual/array/from';
import 'core-js/actual/array/flat-map';
import 'core-js/actual/structured-clone';

Promise.try(() => 42).then(it => console.log(it)); // => 42

Array.from(new Set([1, 2, 3]).union(new Set([3, 4, 5]))); // => [1, 2, 3, 4, 5]

[1, 2].flatMap(it => [it, it]); // => [1, 1, 2, 2]

Iterator.concat([1, 2], function * (i) { while (true) yield i++; }(3))
  .drop(1).take(5)
  .filter(it => it % 2)
  .map(it => it ** 2)
  .toArray(); // => [9, 25]

structuredClone(new Set([1, 2, 3])); // => new Set([1, 2, 3])
```

--------------------------------

### Global Symbol Registry with Symbol.for and Symbol.keyFor

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/symbol.md

Shows how to use `Symbol.for` to create or retrieve a symbol from a global registry and `Symbol.keyFor` to get its associated string key.

```javascript
let symbol = Symbol.for('key');
symbol === Symbol.for('key'); // => true
Symbol.keyFor(symbol);        // => 'key'
```

--------------------------------

### Babel Preset Env: 'entry' mode example

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/usage.md

When using `useBuiltIns: 'entry'`, imports of `core-js/stable` are replaced with specific module imports required for the target environment.

```typescript
import 'core-js/stable';
```

```typescript
import 'core-js/modules/es.array.unscopables.flat';
import 'core-js/modules/es.array.unscopables.flat-map';
import 'core-js/modules/es.object.from-entries';
import 'core-js/modules/web.immediate';
```

--------------------------------

### Basic Structured Clone Examples

Source: https://github.com/zloirock/core-js/blob/master/README.md

Illustrates basic deep cloning of an array of objects and a circular object using structuredClone. Verifies that the cloned object and its properties are distinct from the original.

```javascript
const structured = [{ a: 42 }];
const sclone = structuredClone(structured);
console.log(sclone);
console.log(structured !== sclone);
console.log(structured[0] !== sclone[0]);
```

```javascript
const circular = {};
circular.circular = circular;
const cclone = structuredClone(circular);
console.log(cclone.circular === cclone);
```

--------------------------------

### Array.prototype.fill() Method

Source: https://github.com/zloirock/core-js/blob/master/README.md

Fills all the elements of an array from a start index to an end index with a static value. Supports optional start and end parameters.

```typescript
  fill(value: any, start?: number, end?: number): this;

```

--------------------------------

### core-js-compat Modules by Entry Point

Source: https://github.com/zloirock/core-js/blob/master/packages/core-js-compat/README.md

Illustrates how to retrieve a map of modules categorized by their core-js entry points.

```javascript
// map of modules by `core-js` entry points:
require('core-js-compat/entries'); // => { [EntryPoint]: Array<ModuleName> }
```

```javascript
// or
require('core-js-compat').entries; // => { [EntryPoint]: Array<ModuleName> }
```

--------------------------------

### Function.isCallable and Function.isConstructor Examples

Source: https://github.com/zloirock/core-js/blob/master/README.md

Provides examples for checking if a value is a callable function or a constructible function (class or constructor function). Useful for runtime type checking and validation.

```javascript
/* eslint-disable prefer-arrow-callback -- example */
Function.isCallable(null);                        // => false
Function.isCallable({});                          // => false
Function.isCallable(function () { /* empty */ }); // => true
Function.isCallable(() => { /* empty */ });       // => true
Function.isCallable(class { /* empty */ });       // => false

Function.isConstructor(null);                        // => false
Function.isConstructor({});                          // => false
Function.isConstructor(function () { /* empty */ }); // => true
Function.isConstructor(() => { /* empty */ });       // => false
Function.isConstructor(class { /* empty */ });       // => true
```

--------------------------------

### String#matchAll Entry Point

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/string-matchall.md

Shows the import path for the String#matchAll proposal when using core-js.

```plaintext
core-js/proposals/string-match-all
```

--------------------------------

### Promise All Example

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/promise.md

Demonstrates Promise.all() which takes an iterable of Promises and returns a single Promise that resolves when all of the Promises in the iterable have resolved, or rejects with the reason of the first Promise that rejects.

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

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

--------------------------------

### Web Standard 'self' Usage Example

Source: https://github.com/zloirock/core-js/blob/master/README.md

Illustrates the usage of the `self` global object to access built-in global properties, such as `Array`. This example verifies that `self.Array` is equivalent to the global `Array`.

```javascript
// eslint-disable-next-line no-restricted-globals -- example
self.Array === Array; // => true
```

--------------------------------

### Reflect.getPrototypeOf

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/reflect.md

Gets the prototype of a specified object.

```APIDOC
## Reflect.getPrototypeOf

### Description
Gets the prototype of a specified object.

### Method
`Reflect.getPrototypeOf(target)`

### Parameters
- **target** (Object) - The object whose prototype to retrieve.

### Response
#### Success Response
- Returns the prototype of the given object, or `null` if the object has no prototype.
```

--------------------------------

### Core-JS Entry Point for Array flat/flatMap

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/array-prototype-flat-flatmap.md

Import path for using Array.prototype.flat and Array.prototype.flatMap via core-js.

```plaintext
core-js/proposals/array-flat-map
```

--------------------------------

### Reflect.get

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/reflect.md

Gets the value of a property on an object.

```APIDOC
## Reflect.get

### Description
Gets the value of a property on an object.

### Method
`Reflect.get(target, propertyKey, receiver)`

### Parameters
- **target** (Object) - The object to retrieve the property from.
- **propertyKey** (PropertyKey) - The name of the property to retrieve.
- **receiver** (any, optional) - The value to use as `this` when retrieving the property's value (useful for getters).

### Response
#### Success Response
- Returns the value of the property.
```

--------------------------------

### Get Required core-js Modules

Source: https://github.com/zloirock/core-js/blob/master/packages/core-js-compat/README.md

Import and use the compat function to get a list of required core-js modules and their target environment versions based on a browserslist query. You can filter modules by inclusion or exclusion and specify the core-js version.

```javascript
import compat from 'core-js-compat';

const {
  list,
  targets,
} = compat({
  targets: '> 1%',
  modules: [
    'core-js/actual',
    'esnext.array.unique-by',
    /^web\./,
  ],
  exclude: [
    'web.atob',
  ],
  version: '3.49',
  inverse: false,
});

console.log(targets);
```

--------------------------------

### Entry Point for Object.getOwnPropertyDescriptors

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/object-getownpropertydescriptors.md

Specifies the import path for using the Object.getOwnPropertyDescriptors polyfill from core-js.

```plaintext
core-js/proposals/object-getownpropertydescriptors
```

--------------------------------

### Reflect.getOwnPropertyDescriptor

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/reflect.md

Gets the own property descriptor of a specified property on an object.

```APIDOC
## Reflect.getOwnPropertyDescriptor

### Description
Gets the own property descriptor of a specified property on an object.

### Method
`Reflect.getOwnPropertyDescriptor(target, propertyKey)`

### Parameters
- **target** (Object) - The object to retrieve the property descriptor from.
- **propertyKey** (PropertyKey) - The name of the property to get the descriptor for.

### Response
#### Success Response
- Returns a property descriptor object for the given property if it exists on the object, otherwise returns `undefined`.
```

--------------------------------

### AsyncIterator Chaining Example

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/asynciterator-helpers.md

Demonstrates chaining multiple AsyncIterator helper methods: drop, take, filter, map, and toArray. This example shows how to process an async iterable by skipping elements, limiting the count, filtering based on a condition, transforming values, and collecting the results into an array.

```javascript
await AsyncIterator.from([1, 2, 3, 4, 5, 6, 7])
  .drop(1)
  .take(5)
  .filter(it => it % 2)
  .map(it => it ** 2)
  .toArray();  // => [9, 25]
```

--------------------------------

### Get Function Name

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/function.md

Retrieves the name of a function. Useful for debugging or introspection.

```javascript
(function foo() { /* empty */ }).name; // => 'foo'
```

--------------------------------

### Entry Point for Array.prototype.includes

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/array-prototype-includes.md

Specifies the import path for the Array.prototype.includes proposal in core-js.

```plaintext
core-js/proposals/array-includes
```

--------------------------------

### Array.prototype.fill

Source: https://github.com/zloirock/core-js/blob/master/README.md

Fills all the elements of an array from a start index to an end index with a static value.

```APIDOC
## Array.prototype.fill

### Description
Fills all the elements of an array from a start index to an end index with a static value.

### Method
`fill(value: any, start?: number, end?: number): this`

### Parameters
#### Path Parameters
- **value** (any) - Required - The value to fill the array with.
- **start** (number) - Optional - The index to start filling from (inclusive).
- **end** (number) - Optional - The index to stop filling at (exclusive).

### Response
#### Success Response (200)
- **this** - The modified array.
```

--------------------------------

### Entry Points for Composite Key and Symbol Modules

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/compositekey-compositesymbol.md

Lists the available entry points for importing the `keys-composition` proposal, including full and pure versions for `composite-key` and `composite-symbol`.

```plaintext
core-js/proposals/keys-composition
core-js(-pure)/full/composite-key
core-js(-pure)/full/composite-symbol
```

--------------------------------

### Entry Point for Math.sumPrecise

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/math-sumprecise.md

Specifies the import path for using the Math.sumPrecise proposal within core-js projects.

```plaintext
core-js/proposals/math-sum
```

--------------------------------

### Reflect.ownKeys Example

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/reflect.md

Demonstrates how Reflect.ownKeys() retrieves all own property keys of an object, including symbols.

```javascript
let object = { a: 1 };
Object.defineProperty(object, 'b', { value: 2 });
object[Symbol('c')] = 3;
Reflect.ownKeys(object); // => ['a', 'b', Symbol(c)]
```

--------------------------------

### Map Upsert

Source: https://github.com/zloirock/core-js/blob/master/README.md

Enables getting or inserting elements into Map and WeakMap with computed values.

```APIDOC
## Map Upsert

### Description
Enables getting or inserting elements into Map and WeakMap, with options for computed values.

### Class
`Map`

### Methods
- `getOrInsert(key: any, value: any): any`
- `getOrInsertComputed(key: any, (key: any) => value: any): any`

### Class
`WeakMap`

### Methods
- `getOrInsert(key: object | symbol, value: any): any`
- `getOrInsertComputed(key: object | symbol, (key: any) => value: any): any`
```

--------------------------------

### JSON stringify example with special characters

Source: https://github.com/zloirock/core-js/blob/master/README.md

Demonstrates JSON.stringify with a character that requires special encoding.

```javascript
JSON.stringify({ '𠮷': ['\uDF06\uD834'] }); // => '{"𠮷":["\\udf06\\ud834"]}'
```

--------------------------------

### RegExp.prototype.toString Call

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/string-regexp.md

Demonstrates how to get the string representation of a RegExp object, including its source and flags.

```javascript
RegExp.prototype.toString.call({ source: 'foo', flags: 'bar' }); // => '/foo/bar'
```

--------------------------------

### Babel Preset Env: 'entry' mode with multiple entry points

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/usage.md

Demonstrates how `useBuiltIns: 'entry'` handles multiple core-js entry points, replacing them with specific module imports for the target environment.

```typescript
import 'core-js/es';
import 'core-js/proposals/set-methods';
import 'core-js/full/set/map';
```

```typescript
import 'core-js/modules/es.array.unscopables.flat';
import 'core-js/modules/es.array.unscopables.flat-map';
import 'core-js/modules/es.object.from-entries';
import 'core-js/modules/esnext.set.difference';
import 'core-js/modules/esnext.set.intersection';
import 'core-js/modules/esnext.set.is-disjoint-from';
import 'core-js/modules/esnext.set.is-subset-of';
import 'core-js/modules/esnext.set.is-superset-of';
import 'core-js/modules/esnext.set.map';
import 'core-js/modules/esnext.set.symmetric-difference';
import 'core-js/modules/esnext.set.union';
```

--------------------------------

### Basic Iterator.range Usage

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/iterator-range.md

Iterates from a start number up to (but not including) an end number. Use this for simple sequential iteration.

```javascript
for (const i of Iterator.range(1, 10)) {
  console.log(i); // => 1, 2, 3, 4, 5, 6, 7, 8, 9
}
```

--------------------------------

### Symbol Basics and Properties

Source: https://github.com/zloirock/core-js/blob/master/README.md

Demonstrates basic Symbol usage, including accessing properties and their non-enumerable nature.

```javascript
console.log(person.getName());            // => 'Vasya'
console.log(person.name);                 // => undefined
console.log(person[Symbol('name')]);      // => undefined, symbols are uniq
for (let key in person) console.log(key); // => nothing, symbols are not enumerable
```

--------------------------------

### Build Packages and Test Bundles

Source: https://github.com/zloirock/core-js/blob/master/CONTRIBUTING.md

Prepares packages and test bundles, necessary for running tests in specific browsers.

```sh
npx run-s prepare bundle
```

--------------------------------

### core-js-compat Modules List for Target Version

Source: https://github.com/zloirock/core-js/blob/master/packages/core-js-compat/README.md

Demonstrates how to obtain a list of core-js modules compatible with a specific core-js version.

```javascript
// the subset of modules which available in the passed `core-js` version:
require('core-js-compat/get-modules-list-for-target-version')('3.49'); // => Array<ModuleName>
```

```javascript
// or
require('core-js-compat').getModulesListForTargetVersion('3.49'); // => Array<ModuleName>
```

--------------------------------

### Importing Set Methods with core-js

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/set-methods.md

This shows the entry point for importing the Set methods proposal (v2) when using the core-js library. Ensure you use the correct path for your project.

```plaintext
core-js/proposals/set-methods-v2
```

--------------------------------

### Import Specific Core-JS Features (Set Example)

Source: https://github.com/zloirock/core-js/blob/master/README.md

Import specific features like 'Set' or its related methods, with options for including proposals or only stable features. Also shows how to import without global namespace pollution.

```ts
// if you want to polyfill `Set`:
// all `Set`-related features, with early-stage ES proposals:
import "core-js/full/set";
```

```ts
// stable required for `Set` ES features, features from web standards and stage 3 ES proposals:
import "core-js/actual/set";
```

```ts
// stable required for `Set` ES features and features from web standards
// (DOM collections iterator in this case):
import "core-js/stable/set";
```

```ts
// only stable ES features required for `Set`:
import "core-js/es/set";
```

```ts
// the same without global namespace pollution:
import Set from "core-js-pure/full/set";
```

```ts
import Set from "core-js-pure/actual/set";
```

```ts
import Set from "core-js-pure/stable/set";
```

```ts
import Set from "core-js-pure/es/set";
```

--------------------------------

### Entry Point for Well-formed Stringify

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/well-formed-jsonstringify.md

This is the import path for using the well-formed JSON.stringify proposal from the core-js library.

```plaintext
core-js/proposals/well-formed-stringify
```

--------------------------------

### Symbol Predicates Usage Example

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/proposals/symbol-predicates.md

Demonstrates how to use Symbol.isRegisteredSymbol to check if a symbol is globally registered and Symbol.isWellKnownSymbol to check for well-known symbols.

```javascript
Symbol.isRegisteredSymbol(Symbol.for('key')); // => true
Symbol.isRegisteredSymbol(Symbol('key')); // => false

Symbol.isWellKnownSymbol(Symbol.iterator); // => true
Symbol.isWellKnownSymbol(Symbol('key')); // => false
```

--------------------------------

### Build Custom core-js Bundle

Source: https://github.com/zloirock/core-js/blob/master/packages/core-js-builder/README.md

Demonstrates how to use the core-js-builder to create a custom bundle. Configure included modules, exclusions, and target environments. The output can be formatted as a bundle, CJS, or ESM, and saved to a specified filename.

```javascript
import builder from 'core-js-builder';

const bundle = await builder({
  // entry / module / namespace / an array of them, by default - all `core-js` modules
  modules: ['core-js/actual', /^esnext\.reflect\./],
  // a blacklist of entries / modules / namespaces, by default - empty list
  exclude: [/^es\.math\./, 'es.number.constructor'],
  // optional browserslist or core-js-compat format query
  targets: '> 0.5%, not dead, ie 9-11',
  // shows summary for the bundle, disabled by default
  summary: {
    // in the console, you could specify required parts or set `true` for enable all of them
    console: { size: true, modules: false },
    // in the comment in the target file, similarly to `summary.console`
    comment: { size: false, modules: true },
  },
  // output format, 'bundle' by default, can be 'cjs' or 'esm', and in this case
  // the result will not be bundled and will contain imports of required modules
  format: 'bundle',
  // optional target filename, if it's missed a file will not be created
  filename: PATH_TO_MY_COREJS_BUNDLE,
});
```

--------------------------------

### Basic structuredClone Usage

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/web-standards/structured-clone.md

Demonstrates the basic usage of structuredClone for cloning an array of objects. Shows that the clone is a deep copy.

```js
const structured = [{ a: 42 }];
const sclone = structuredClone(structured);
console.log(sclone);
console.log(structured !== sclone);
console.log(structured[0] !== sclone[0]);
```

--------------------------------

### Promise Finally Example

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/promise.md

Shows how Promise.finally() executes a callback regardless of whether the Promise is fulfilled or rejected, useful for cleanup operations.

```js
Promise.resolve(42).finally(() => console.log('You will see it anyway'));

Promise.reject(42).finally(() => console.log('You will see it anyway'));
```

--------------------------------

### Promise Resolve and Reject Examples

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/promise.md

Illustrates using Promise.resolve() to create a resolved Promise with a value and Promise.reject() to create a rejected Promise. Also shows resolving a Promise with another Promise.

```js
const getJson = () => new Promise(resolve => {
  resolve({ message: "Hello, world!", success: true });
});

Promise.resolve(42).then(x => console.log(x));         // -> 42
Promise.reject(42).catch(error => console.log(error)); // -> 42

Promise.resolve(getJson()); // => ES promise
```

--------------------------------

### Bind Console Method

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/function.md

Binds the 'log' method of the console object with a pre-filled argument. This example demonstrates partial application of a method.

```javascript
console.log.bind(console, 42)(43); // -> 42 43
```

--------------------------------

### Array.prototype.copyWithin() Method

Source: https://github.com/zloirock/core-js/blob/master/README.md

Copies a sequence of elements within an array to another position in the same array. Supports target, start, and optional end parameters.

```typescript
  copyWithin(target: number, start: number, end?: number): this;

```

--------------------------------

### Using Promise.withResolvers

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/promise.md

Demonstrates the creation of a Promise with explicit resolve and reject methods exposed.

```javascript
const d = Promise.withResolvers();
d.resolve(42);
d.promise.then(console.log); // -> 42
```

--------------------------------

### Fill Array with a Static Value

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/array.md

The fill method changes all elements in an array to a static value, from a start index up to (but not including) an end index.

```javascript
Array(5).fill(42); // => [42, 42, 42, 42, 42]
```

--------------------------------

### Basic Promise Chaining Example

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/features/ecmascript/promise.md

Demonstrates creating a Promise that resolves after a delay and chaining multiple .then() calls to handle asynchronous operations sequentially. Includes error handling with .catch().

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

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

--------------------------------

### Map Iteration Example

Source: https://github.com/zloirock/core-js/blob/master/README.md

Illustrates various ways to iterate over a Map, including using `for...of` loops with entries, values, keys, and explicitly with `map.entries()`. Shows how to access both keys and values during iteration.

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

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

--------------------------------

### Transpiled Array Includes with Babel Runtime CoreJS3

Source: https://github.com/zloirock/core-js/blob/master/docs/2019-03-19-core-js-3-babel-and-a-look-into-the-future.md

This example shows how `array.includes(something)` is transpiled using `@babel/runtime-corejs3` to support instance methods.

```javascript
array.includes(something);
```

```javascript
import _includesInstanceProperty from "@babel/runtime-corejs3/core-js-stable/instance/includes";

_includesInstanceProperty(array).call(array, something);
```

--------------------------------

### DataView get / set Uint8Clamped methods

Source: https://github.com/zloirock/core-js/blob/master/README.md

Adds `getUint8Clamped` and `setUint8Clamped` methods to the DataView prototype for handling clamped 8-bit unsigned integers.

```APIDOC
## DataView get / set Uint8Clamped methods

### Description
Adds `getUint8Clamped` and `setUint8Clamped` methods to the DataView prototype.

### Methods
- `DataView.prototype.getUint8Clamped(offset: any): uint8`
- `DataView.prototype.setUint8Clamped(offset: any, value: any): void`

### Examples
```js
const view = new DataView(new ArrayBuffer(1));
view.setUint8Clamped(0, 100500);
console.log(view.getUint8Clamped(0)); // => 255
```
```

--------------------------------

### Disable Core-js Postinstall Message

Source: https://github.com/zloirock/core-js/blob/master/docs/web/docs/usage.md

Prevent the core-js postinstall message from appearing during npm installation by setting environment variables or using npm loglevel.

```sh
ADBLOCK=true npm install
```

```sh
DISABLE_OPENCOLLECTIVE=true npm install
```

```sh
npm install --loglevel silent
```

--------------------------------

### Run Linting

Source: https://github.com/zloirock/core-js/blob/master/CONTRIBUTING.md

Execute the linter to check code style compliance.

```sh
npm run lint
```
Tokens:
Raw