JS: New Features 2016 to 2021

Since 2015, new features are added to JavaScript the language each year.

JS2015

2015 Features

JS2016

• Array.prototype.includes
• The power operator **. Example, 3 ** 2 === 9. 〔see Operators〕

JS2017

• Object.entries
• Object.values
• Object.getOwnPropertyDescriptors
• String.prototype.padStart
• String.prototype.padEnd
• async keyword for functions and await keyword. (xtodo )

JS2018

Destructure object rest properties

For example, we have let { c, ...remainProperties } = { a:1, b:2, c:3 };, then c is 3. remainProperties is { a:1, b: 2 } . See: • Destructuring Assignment • Function Argument Destructure

Spread operator for object literal

For example, { ...{ a:1, b:2}, c:3 } becomes { a:1, b:2, c:3 } . See: Spread Operator

Regex Features

• The dotAll flag: s, make the dot . also match newline characters. See dotAll Flag
• Match characters by Unicode character property: \p{PropertyValue} and \P{PropertyValue}. See RegExp Unicode Property
• Named capture group. See RegExp Syntax
• lookbehind assertions. See RegExp Syntax

promise finally, async iteration

• Promise.prototype.finally. (xtodo )
• Asynchronous iteration. (xtodo )

JS2019

• Array.prototype.flat
• Array.prototype.flatMap
• Object.fromEntries
• String.prototype.trimStart
• String.prototype.trimEnd
• Symbol.prototype.description 〔see Symbol.prototype〕

JS2020

globalThis

A variable that is alias to the Global Object the Global Object

??

Nullish Coalescing Operator

?.

Optional Chaining Operator

String.prototype.matchAll

String.prototype.matchAll

Property Order Guaranteed

Now object property's order is guaranteed by spec.

bigint

xtodo

const x = 10n;
console.log( typeof x === "bigint" ); // true

• Value Types
• Number Object

dynamic import

import * as xyz from "./xyz.js";

Import/Export

import.meta

export {abc} from "./xyz.js";
export * from "./xyz.js";

import() syntax

Promise.allSettled

Promise Tutorial

JS2021

Number Separator

Numbers can have lowline _ between digits. For example, you can write 1_000.

Logical AND assignment operator x &&= y

Assigns y to x if Boolean(x) eval to true. see JS: Operators

Logical OR assignment operator x ||= y

Assigns y to x if Boolean(x) eval to false.

Logical Nullish assignment operator x ??= y

Assigns y to x if x is null or undefined

• String.prototype.replaceAll
• Promise.any
• weak reference