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Compile the new function bind operator
::
to ES5.
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)
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)%3B%20%2F%2F%20prints%20'10'%0A%2F%2F%20bigBox%3A%3AgetWeight()%20is%20equivalent%20to%20getWeight.call(bigBox)%0A%0A%2F%2F%20Can%20be%20chained%3A%0Afunction%20add(val)%20%7B%20return%20this%20%2B%20val%3B%20%7D%0A%0Aconsole.log(bigBox%3A%3AgetWeight()%3A%3Aadd(5))%3B%20%2F%2F%20prints%20'15')
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%0A%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%3A%3Amap(node%20%3D%3E%20node.href)%0A%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%3A%3Afilter(href%20%3D%3E%20href.substring(0%2C%205)%20%3D%3D%3D%20'https')%3B%0A%0Aconsole.log(sslUrls)%3B%0A)
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);
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));
npm install --save-dev babel-plugin-transform-function-bind
.babelrc
(Recommended).babelrc
{
"plugins": ["transform-function-bind"]
}
babel --plugins transform-function-bind script.js
require("babel-core").transform("code", {
plugins: ["transform-function-bind"]
});