@babel/plugin-proposal-function-bind
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
With a configuration file (Recommended)
{
"plugins": ["@babel/plugin-proposal-function-bind"]
}
Via CLI
babel --plugins @babel/plugin-proposal-function-bind script.js
Via Node API
require("@babel/core").transform("code", {
plugins: ["@babel/plugin-proposal-function-bind"]
});