@babel/plugin-proposal-function-bind

What is @babel/plugin-proposal-function-bind?

@babel/plugin-proposal-function-bind is a Babel plugin that allows you to use the bind operator (::) in your JavaScript code. This operator is a syntactic sugar for function binding, making it easier to bind functions to a specific context.

What are @babel/plugin-proposal-function-bind's main functionalities?

Function Binding

This feature allows you to bind a function to a specific context using the bind operator (::). In this example, the greet function is bound to the obj context, so it correctly logs 'Hello, Alice!'.

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

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

Partial Application

This feature allows you to create partially applied functions using the bind operator (::). In this example, the add function is partially applied with the value 5, creating a new function add5 that adds 5 to its argument.

function add(a, b) {
  return a + b;
}

const add5 = add.bind(null, 5);
console.log(add5(10)); // Output: 15

Other packages similar to @babel/plugin-proposal-function-bind

lodash

Lodash is a utility library that provides a wide range of functions for common programming tasks, including function binding. The _.bind method in Lodash can be used to bind functions to a specific context, similar to the bind operator in @babel/plugin-proposal-function-bind.

ramda

Ramda is a functional programming library for JavaScript that provides a variety of utility functions, including function binding. The R.bind method in Ramda can be used to bind functions to a specific context, offering similar functionality to the bind operator in @babel/plugin-proposal-function-bind.

README

@babel/plugin-proposal-function-bind

Compile the new function bind operator :: to ES5.

Detail

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

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

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

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

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'

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);

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-proposal-function-bind

Usage

Via .babelrc (Recommended)

.babelrc

{
  "plugins": ["@babel/proposal-function-bind"]
}

Via CLI

babel --plugins @babel/proposal-function-bind script.js

Via Node API

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

References

• Proposal
• Babel Blog: Function Bind Syntax