ECMAScript 2020
New Features in JavaScript 2020
| Feature | Description |
|---|---|
| BigInt | Stores values too big to store in a JavaScript number |
| String matchAll() | Searchs for all occurrences of a string in a string |
| Promise.allSettled() | Takes promises as input and returns a single promise |
| Dynamic Import | Loads JavaScript modules at runtime |
| globalThis | Refers to the global object independent of code environment |
| import.meta | Returns an object indicating the base URL of a module |
| Namespace Exports | Export a full namespace from a module without having to import it first |
New JavaScript Operators in 2020
| Oper | Description |
|---|---|
| ?? | Nullish coalescing returns the first argument not nullish |
| ?. | Optional chaining returns undefined if an object is undefined or null |
| &&= | Logical AND assignment assigns the second value if the first value is true |
| ||= | Logical OR assignment assigns the second value if the first value is false |
| ??= | Nullish coalescing assignment assigns the second value if the first value is undefined or null |
Browser Support
ECMAScript 2020 is supported in all modern browsers since April 2021.
| Chrome 80 |
Edge 80 |
Firefox 80 |
Safari 14.1 |
Opera 67 |
| Feb 2020 | Feb 2020 | Aug 2020 | Apr 2021 | Mar 2020 |
JavaScript BigInt
JavaScript BigInt variables are used to store big integer values
that are too big to be represented by a a normal JavaScript Number.
JavaScript integers are only accurate up to about 15 digits.
Integer Example
let y = 9999999999999999; // too big
BigInt Example
let y = 9999999999999999n;
To create a BigInt, append n to the end of an integer or call
BigInt():
Example
let y = BigInt(1234567890123456789012345)
The JavaScript typeof a BigInt is "bigint":
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.
If the parameter is a regular expression, the global flag (g) must be set set, otherwise a TypeError is thrown.
If you want to search case insensitive, the insensitive flag (i) must be set:
Note
ES2021 introduced the string method replaceAll().
The Nullish Coalescing Operator (??)
The ?? operator returns the first operand if it is not nullish.
Otherwise it returns the second.
The ?? operator returns the second operand if the first operand is nullish.
Nullish is a word for describing null or undefined.
The ?? operator is used to provide default values and is distinct from the logical OR operator ||
because it only treats null and undefined as "nullish" and ignores other "falsy" values
like 0 or an empty string.
The Optional Chaining Operator (?.)
The Optional Chaining Operator returns undefined if an object property is
undefined or null (instead of throwing an error).
Example
let name = car?.name;
Optional chaining not only works on object properties, but also on function calls and arrays.
Function Calls
| Use Case | Syntax | Behavior |
|---|---|---|
| Safe function call | obj.method?.() | Returns undefined if method does not exist |
| Return handling | let x = fn?.() | x is undefined if fn does not exist |
Arrays
| Use Case | Syntax | Returns |
|---|---|---|
| Safe element access | arr?.[2] | undefined if arr is null
or undefined |
| Safe property on element | arr?.[1]?.name | Returns undefined safely |
| Safe method call | arr?.map(fn) | Returns undefined if arr does not exist |
| Default value fallback | arr?.[0] ?? "N/A" | Returns "N/A" if arr or element is missing |
The &&= Operator
The Logical AND Assignment Operator is used between two values.
If the first value is true, the second value is assigned.
The ||= Operator
The Logical OR Assignment Operator is used between two values.
If the first value is false, the second value is assigned.
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.
JavaScript Promise.allSettled()
The Promise.allSettled() method returns a single Promise from a list of promises.
Example
const myPromise1 = new Promise((resolve, reject) => {
setTimeout(resolve, 200, "King");
});
// Create another Promise
const myPromise2 = new Promise((resolve, reject) => {
setTimeout(resolve, 100, "Queen");
});
// Settle All
Promise.allSettled([myPromise1, myPromise2]).then((results) =>
results.forEach((x) => myDisplay(x.status)),
);
Note
Promise.allSettled() means "Just run all promises. I don't care about the results".
JavaScript Dynamic Import
Dynamic Import is a way to load JavaScript modules at runtime, rather than at the start of your program.
Syntax
- The argument must be a string or expression that resolves to a path
- You must run the import inside a module script (<script type="module">)
Unlike static imports (which must appear at the top of a file), dynamic imports can be used anywhere - inside functions, conditionals, event handlers, etc.
| Type | Example | When Loaded |
|---|---|---|
| Static | import { add } from './math.js'; |
At load time |
| Dynamic | const math = await import('./math.js'); |
When needed |
JavaScript Global This
globalThis provides a standard way to access the global object,
regardless of the environment your the code runs in: In the browser, Node.js, in a Web Worker, or another JS runtime.
The global object is the top-level object in a JavaScript environment:
- In browsers, it is window.
- In Node.js, it is global.
- In Web Workers, it is self.
Many environments have their own name for the this object. This caused compatibility issues for code meant to run everywhere.
globalThis was introduced in ECMAScript 2020
(ES11) to solve that problem. It is a unified reference to the global object, no matter the environment.
Examples
globalThis === global); // true in Node.js
Example
Defining a truly global variable:
Previously, developers had to use workarounds like:
Example
if (typeof self !== 'undefined') return self;
if (typeof window !== 'undefined') return window;
if (typeof global !== 'undefined') return global;
throw new Error('Cannot find global object');
};
With globalThis, that is no longer needed.
JavaScript import.meta
import.meta returns an object containing the base URL of a module.
Module Namespace Exports
With module namespace exports, you can re-export an entire namespace from your own module, without having to import it first.
Example
Before:
export * from "./utils.js";
// consumers can use:
import { add } from "./math.js";
Now:
export * as utils from "./utils.js";
// consumers can use:
import { utils } from "./math.js";