babel/packages/babel-plugin-transform-function-bind

babel-plugin-transform-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-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