autobind decorator

A class or method decorator which binds methods to the instance so this is always correct, even when the method is detached.

This is particularly useful for situations like React components, where you often pass methods as event handlers and would otherwise need to .bind(this).

1// Before:
2<button onClick={ this.handleClick.bind(this) }></button>
3
4// After:
5<button onClick={ this.handleClick }></button>

As decorators are a part of future ECMAScript standard they can only be used with transpilers such as Babel.

Installation

npm install autobind-decorator

Supported platforms

Output

We target IE11+ browsers (see out browserslist) with the following caveats:

main: ES5

module: ES5 + ES modules to enable tree shaking

es: modern JS

On consuming modern JS, you can transpile the script to your target environment (@babel/preset-env is recommended) to minimise the cost. For more details, please read https://babeljs.io/blog/2018/06/26/on-consuming-and-publishing-es2015+-packages.

Dev

node 8.10+ with latest npm

Babel 6 users (legacy only)

The implementation of the decorator transform is currently on hold as the syntax is not final. If you would like to use this project with Babel 6, you may use babel-plugin-transform-decorators-legacy which implement Babel 5 decorator transform for Babel 6.

Babel 7 users

Legacy

Babel 7's @babel/plugin-proposal-decorators officially supports the same logic that babel-plugin-transform-decorators-legacy has, but integrates better with Babel 7's other plugins. You can enable this with

1{
2  "plugins": [
3    ["@babel/plugin-proposal-decorators", { "legacy": true }],
4  ]
5}

in your Babel configuration. Note that legacy: true is specifically needed if you want to get the same behavior as transform-decorators-legacy because there are newer versions of the decorator specification coming out, and they do not behave the same way.

Modern

For now, you'll have to use one of the solutions in https://github.com/nicolo-ribaudo/legacy-decorators-migration-utility. We are trying to keep this module up-to-date with the latest spec. For more details, please read https://babeljs.io/blog/2018/09/17/decorators.

TypeScript users

This package will work out of the box with TypeScript (no Babel needed) and includes the .d.ts typings along with it.

Examples

Recommended way to bind a method

Use @boundMethod on a method

1import {boundMethod} from 'autobind-decorator'
2
3class Component {
4  constructor(value) {
5    this.value = value
6  }
7
8  @boundMethod
9  method() {
10    return this.value
11  }
12}
13
14let component = new Component(42)
15let method = component.method // .bind(component) isn't needed!
16method() // returns 42

@boundMethod makes method into an auto-bound method, replacing the explicit bind call later.

Discouraged approaches

Magical @autobind that can be used on both classes and methods

1import autobind from 'autobind-decorator'
2
3class Component {
4  constructor(value) {
5    this.value = value
6  }
7
8  @autobind
9  method() {
10    return this.value
11  }
12}
13
14let component = new Component(42)
15let method = component.method // .bind(component) isn't needed!
16method() // returns 42
17
18// Also usable on the class to bind all methods
19// Please see performance section below if you decide to autobind your class
20@autobind
21class Component { }

Use @boundClass on a class

Please see performance section below if you decide to autobind your class

1import {boundClass} from 'autobind-decorator'
2
3@boundClass
4class Component {
5  constructor(value) {
6    this.value = value
7  }
8
9  method() {
10    return this.value
11  }
12}
13
14let component = new Component(42)
15let method = component.method // .bind(component) isn't needed!
16method() // returns 42

Performance

autobind (boundMethod) on a method is lazy and is only bound once. :thumbsup:

However,

It is unnecessary to do that to every function. This is just as bad as autobinding (on a class). You only need to bind functions that you pass around. e.g. onClick={this.doSomething}. Or fetch.then(this.handleDone) -- Dan Abramov‏

You should avoid using autobind (boundClass) on a class. :thumbsdown:

I was the guy who came up with autobinding in older Reacts and I'm glad to see it gone. It might save you a few keystrokes but it allocates functions that'll never be called in 90% of cases and has noticeable performance degradation. Getting rid of autobinding is a good thing -- Peter Hunt

Alternative

• Class field declarations - This is also not standard JavaScript yet (Stage 3).