122 lines
2.4 KiB
Markdown
122 lines
2.4 KiB
Markdown
# @babel/plugin-proposal-function-bind
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> Compile the new function bind operator `::` to ES5.
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## Detail
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```js
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obj::func
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// is equivalent to:
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func.bind(obj)
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::obj.func
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// is equivalent to:
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obj.func.bind(obj)
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obj::func(val)
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// is equivalent to:
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func.call(obj, val)
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::obj.func(val)
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// is equivalent to:
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obj.func.call(obj, val)
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```
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## Example
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### Basic
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```js
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const box = {
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weight: 2,
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getWeight() { return this.weight; },
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};
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const { getWeight } = box;
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console.log(box.getWeight()); // prints '2'
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const bigBox = { weight: 10 };
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console.log(bigBox::getWeight()); // prints '10'
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// Can be chained:
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function add(val) { return this + val; }
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console.log(bigBox::getWeight()::add(5)); // prints '15'
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```
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### Using with `document.querySelectorAll`
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It can be very handy when used with `document.querySelectorAll`:
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```js
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const { map, filter } = Array.prototype;
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let sslUrls = document.querySelectorAll('a')
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::map(node => node.href)
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::filter(href => href.substring(0, 5) === 'https');
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console.log(sslUrls);
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```
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`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:
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```js
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const { map, filter } = Array.prototype;
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let sslUrls = document.querySelectorAll('a');
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sslUrls = map.call(sslUrls, node => node.href);
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sslUrls = filter.call(sslUrls, href => href.substring(0, 5) === 'https');
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console.log(sslUrls);
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```
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### Auto self binding
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When nothing is specified before the `::` operator, the function is bound to its object:
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```js
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$('.some-link').on('click', ::view.reset);
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// is equivalent to:
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$('.some-link').on('click', view.reset.bind(view));
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```
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## Installation
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```sh
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npm install --save-dev @babel/plugin-proposal-function-bind
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```
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## Usage
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### Via `.babelrc` (Recommended)
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**.babelrc**
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```json
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{
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"plugins": ["@babel/proposal-function-bind"]
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}
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```
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### Via CLI
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```sh
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babel --plugins @babel/proposal-function-bind script.js
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```
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### Via Node API
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```javascript
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require("@babel/core").transform("code", {
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plugins: ["@babel/proposal-function-bind"]
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});
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```
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## References
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* [Proposal](https://github.com/zenparsing/es-function-bind)
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* [Babel Blog: Function Bind Syntax](/blog/2015/05/14/function-bind)
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