autobind-decorator

What is autobind-decorator?

The `autobind-decorator` npm package provides a decorator for automatically binding methods to their class instance. This is particularly useful in JavaScript and TypeScript classes where you want to ensure that methods retain the correct `this` context, especially when passing them as callbacks.

What are autobind-decorator's main functionalities?

Automatic Method Binding

This feature allows you to automatically bind class methods to the instance of the class. In the example, the `getValue` method is bound to the instance of `MyClass`, ensuring that `this.value` correctly refers to the instance's `value` property even when the method is called as a standalone function.

class MyClass {
  constructor() {
    this.value = 42;
  }

  @autobind
  getValue() {
    return this.value;
  }
}

const instance = new MyClass();
const getValue = instance.getValue;
console.log(getValue()); // 42

Other packages similar to autobind-decorator

core-decorators

The `core-decorators` package provides a collection of decorators, including an `autobind` decorator. It offers a broader set of decorators for various use cases, such as `@debounce`, `@memoize`, and `@readonly`, making it a more versatile choice if you need multiple types of decorators.

lodash-decorators

The `lodash-decorators` package offers a set of decorators based on lodash functions, including an `autobind` decorator. It is useful if you are already using lodash in your project and want to leverage its utility functions in a decorator form.

typescript-decorators

The `typescript-decorators` package provides a set of decorators specifically designed for TypeScript. It includes an `autobind` decorator and other useful decorators for TypeScript development, making it a good choice for TypeScript projects.

README

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).

// Before:
<button onClick={ this.handleClick.bind(this) }></button>

// After:
<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

{
  "plugins": [
    ["@babel/plugin-proposal-decorators", { "legacy": true }],
  ]
}

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

import {boundMethod} from 'autobind-decorator'

class Component {
  constructor(value) {
    this.value = value
  }

  @boundMethod
  method() {
    return this.value
  }
}

let component = new Component(42)
let method = component.method // .bind(component) isn't needed!
method() // 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

import autobind from 'autobind-decorator'

class Component {
  constructor(value) {
    this.value = value
  }

  @autobind
  method() {
    return this.value
  }
}

let component = new Component(42)
let method = component.method // .bind(component) isn't needed!
method() // returns 42

// Also usable on the class to bind all methods
// Please see performance section below if you decide to autobind your class
@autobind
class Component { }

Use @boundClass on a class

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

import {boundClass} from 'autobind-decorator'

@boundClass
class Component {
  constructor(value) {
    this.value = value
  }

  method() {
    return this.value
  }
}

let component = new Component(42)
let method = component.method // .bind(component) isn't needed!
method() // 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).