babel-plugin-transform-function-bind

What is babel-plugin-transform-function-bind?

The babel-plugin-transform-function-bind package is a Babel plugin that allows you to use the bind operator (::) in your JavaScript code. This operator provides a shorthand for binding functions to a specific context, making your code more concise and readable.

What are babel-plugin-transform-function-bind's main functionalities?

Function Binding

This feature allows you to bind a function to a specific context using the :: operator. In the example, the greet function is bound to the obj context, ensuring that this.name refers to 'Alice' when the function is called.

const obj = {
  name: 'Alice',
  greet() {
    console.log(`Hello, ${this.name}!`);
  }
};

const greet = obj::obj.greet;
greet(); // Output: Hello, Alice!

Method Extraction

This feature allows you to extract a method from an object and bind it to a different context. In the example, the greet method is extracted from obj and then called with a different context, resulting in 'Hello, Charlie!'.

const obj = {
  name: 'Bob',
  greet() {
    console.log(`Hello, ${this.name}!`);
  }
};

const greet = ::obj.greet;
greet.call({ name: 'Charlie' }); // Output: Hello, Charlie!

Other packages similar to babel-plugin-transform-function-bind

babel-plugin-transform-class-properties

This package allows you to use class properties in your JavaScript code. While it doesn't provide the same function binding capabilities as babel-plugin-transform-function-bind, it does offer a way to define methods and properties directly within a class, which can sometimes be used to achieve similar results.

README

babel-plugin-transform-function-bind

Compile the new function bind operator :: to ES5.

Detail

obj::func
// is equivalent to:
func.bind(obj)

obj::func(val)
// is equivalent to:
func.call(obj, val)

::obj.func(val)
// is equivalent to:
func.call(obj, val)

Try in REPL

Example

Basic

const box = {
  weight: 2,
  getWeight() { return this.weight; },
};

const { getWeight } = box;

console.log(box.getWeight()); // prints '2'

const bigBox = { weight: 10 };
console.log(bigBox::getWeight()); // prints '10'

// Can be chained:
function add(val) { return this + val; }

console.log(bigBox::getWeight()::add(5)); // prints '15'

Try in REPL

Using with document.querySelectorAll

It can be very handy when used with document.querySelectorAll:

const { map, filter } = Array.prototype;

let sslUrls = document.querySelectorAll('a')
                ::map(node => node.href)
                ::filter(href => href.substring(0, 5) === 'https');

console.log(sslUrls);

Try in REPL

document.querySelectorAll returns a NodeList element which is not a plain array, so you normally can't use the map function on it, and have to use it this way: Array.prototype.map.call(document.querySelectorAll(...), node => { ... }). The above code using the :: will work because it is equivalent to:

const { map, filter } = Array.prototype;

let sslUrls = document.querySelectorAll('a');
sslUrls = map.call(sslUrls, node => node.href);
sslUrls = filter.call(sslUrls, href => href.substring(0, 5) === 'https');

console.log(sslUrls);

Auto self binding

When nothing is specified before the :: operator, the function is bound to its object:

$('.some-link').on('click', ::view.reset);
// is equivalent to:
$('.some-link').on('click', view.reset.bind(view));

Installation

npm install --save-dev babel-plugin-transform-function-bind

Usage

Via .babelrc (Recommended)

.babelrc

{
  "plugins": ["transform-function-bind"]
}

Via CLI

babel --plugins transform-function-bind script.js

Via Node API

require("babel-core").transform("code", {
  plugins: ["transform-function-bind"]
});

References

• Proposal
• Babel Blog: Function Bind Syntax