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JavaScript. W3Schools in English. Lessons for beginners

Ua

ECMAScript 2020

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JavaScript Version Numbers

Old JS versions are named by numbers: ES5 (2009) and ES6 (2015).

From 2016, versions are named by year: ECMAScript 2016, 2017, 2018, 2019, ...

New Features in ES2020

Warning

These features are relatively new.

Older browsers may need an alternative code (Polyfill)

JavaScript BigInt

JavaScript BigInt variables are used to store big integer values that are too big to be represented by a normal JavaScript Number.

JavaScript's integers are only accurate up to about 15 digits.

Integer Example

let x = 999999999999999;
let y = 9999999999999999; // too big
Try it Yourself »

BigInt Example

let x = 9999999999999999;
let y = 9999999999999999n;
Try it Yourself »

To create a BigInt, append n to the end of an integer or call BigInt():

Example

let x = 1234567890123456789012345n;
let y = BigInt(1234567890123456789012345)
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The JavaScript typeof a BigInt is "bigint":

Example

let x = BigInt(999999999999999);
let type = typeof x;
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BigInt is supported in all modern browsers since September 2020:

Chrome 67 Edge 79 Firefox 68 Safari 14 Opera 54
May 2018 Jan 2020 Jul 2019 Sep 2020 Jun 2018

JavaScript String matchAll()

Before ES2020 there was no string method that could be used to search for all occurrences of a string in a string.

Example

const iterator = text.matchAll("Cats");
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If the parameter is a regular expression, the global flag (g) must be set; otherwise a TypeError is thrown.

Example

const iterator = text.matchAll(/Cats/g);
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If you want to search case-insensitive, the insensitive flag (i) must be set:

Example

const iterator = text.matchAll(/Cats/gi);
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Note

ES2021 introduced the string method replaceAll().

The Nullish Coalescing Operator (??)

The ?? operator returns the first argument if it is not nullish (null or undefined).

Otherwise, it returns the second.

Example

let name = null;
let text = "missing";
let result = name ?? text;
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The nullish operator is supported in all modern browsers since March 2020:

Chrome 80 Edge 80 Firefox 72 Safari 13.1 Opera 67
Feb 2020 Feb 2020 Jan 2020 Mar 2020 Mar 2020

The Optional Chaining Operator (?.)

The Optional Chaining Operator returns undefined if an object is undefined or null (instead of throwing an error).

Example

const car = {type:"Fiat", model:"500", color:"white"};
let name = car?.name;
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The ?.= operator is supported in all modern browsers since March 2020:

Chrome 80 Edge 80 Firefox 74 Safari 13.1 Opera 67
Feb 2020 Feb 2020 Mar 2020 Mar 2020 Mar 2020

The &&= Operator

The Logical AND Assignment Operator is used between two values.

If the first value is true, the second value is assigned.

Logical AND Assignment Example

let x = 10;
x &&= 5;
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The &&= operator is supported in all modern browsers since September 2020:

Chrome 85 Edge 85 Firefox 79 Safari 14 Opera 71
Aug 2020 Aug 2020 Mar 2020 Sep 2020 Sep 2020

The ||= Operator

The Logical OR Assignment Operator is used between two values.

If the first value is false, the second value is assigned.

Logical OR Assignment Example

let x = 10;
x ||= 5;
Try it Yourself »

The ||= operator is supported in all modern browsers since September 2020:

Chrome 85 Edge 85 Firefox 79 Safari 14 Opera 71
Aug 2020 Aug 2020 Mar 2020 Sep 2020 Sep 2020

The ??= Operator

The Nullish Coalescing Assignment Operator is used between two values.

If the first value is undefined or null, the second value is assigned.

Nullish Coalescing Assignment Example

let x;
x ??= 5;
Try it Yourself »

The ??= operator is supported in all modern browsers since September 2020:

Chrome 85 Edge 85 Firefox 79 Safari 14 Opera 71
Aug 2020 Aug 2020 Mar 2020 Sep 2020 Sep 2020
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