1 | # babel-plugin-transform-function-bind
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2 |
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3 | > Compile the new function bind operator `::` to ES5.
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4 |
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5 | ## Detail
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6 |
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7 | ```js
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8 | obj::func
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9 | // is equivalent to:
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10 | func.bind(obj)
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11 |
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12 | obj::func(val)
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13 | // is equivalent to:
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14 | func.call(obj, val)
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15 |
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16 | ::obj.func(val)
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17 | // is equivalent to:
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18 | func.call(obj, val)
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19 | ```
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20 |
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21 | [Try in REPL](http://babeljs.io/repl/#?evaluate=true&presets=es2015%2Cstage-0&code=obj%3A%3Afunc%3B%0A%0Aobj%3A%3Afunc(val)%3B%0A%0A%3A%3Aobj.func(val)%3B)
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22 |
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23 | ## Example
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24 |
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25 | ### Basic
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26 |
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27 | ```js
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28 | const box = {
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29 | weight: 2,
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30 | getWeight() { return this.weight; },
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31 | };
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32 |
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33 | const { getWeight } = box;
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34 |
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35 | console.log(box.getWeight()); // prints '2'
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36 |
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37 | const bigBox = { weight: 10 };
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38 | console.log(bigBox::getWeight()); // prints '10'
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39 |
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40 | // Can be chained:
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41 | function add(val) { return this + val; }
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42 |
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43 | console.log(bigBox::getWeight()::add(5)); // prints '15'
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44 | ```
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45 |
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46 | [Try in REPL](http://babeljs.io/repl/#?evaluate=true&presets=es2015%2Cstage-0&code=const%20box%20%3D%20%7B%0A%20%20weight%3A%202%2C%0A%20%20getWeight()%20%7B%20return%20this.weight%3B%20%7D%2C%0A%7D%3B%0A%0Aconst%20%7B%20getWeight%20%7D%20%3D%20box%3B%0A%0Aconsole.log(box.getWeight())%3B%20%2F%2F%20prints%20'2'%0A%0Aconst%20bigBox%20%3D%20%7B%20weight%3A%2010%20%7D%3B%0Aconsole.log(bigBox%3A%3AgetWeight())%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')
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47 |
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48 | ### Using with `document.querySelectorAll`
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49 |
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50 | It can be very handy when used with `document.querySelectorAll`:
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51 |
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52 | ```js
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53 | const { map, filter } = Array.prototype;
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54 |
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55 | let sslUrls = document.querySelectorAll('a')
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56 | ::map(node => node.href)
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57 | ::filter(href => href.substring(0, 5) === 'https');
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58 |
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59 | console.log(sslUrls);
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60 | ```
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61 |
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62 | [Try in REPL](http://babeljs.io/repl/#?evaluate=true&presets=es2015%2Cstage-0&code=%0Aconst%20%7B%20map%2C%20filter%20%7D%20%3D%20Array.prototype%3B%0A%0Alet%20sslUrls%20%3D%20document.querySelectorAll('a')%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)
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63 |
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64 | `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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65 |
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66 | ```js
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67 | const { map, filter } = Array.prototype;
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68 |
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69 | let sslUrls = document.querySelectorAll('a');
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70 | sslUrls = map.call(sslUrls, node => node.href);
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71 | sslUrls = filter.call(sslUrls, href => href.substring(0, 5) === 'https');
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72 |
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73 | console.log(sslUrls);
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74 | ```
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75 |
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76 | ### Auto self binding
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77 | When nothing is specified before the `::` operator, the function is bound to its object:
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78 |
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79 | ```js
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80 | $('.some-link').on('click', ::view.reset);
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81 | // is equivalent to:
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82 | $('.some-link').on('click', view.reset.bind(view));
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83 | ```
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84 |
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85 | ## Installation
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86 |
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87 | ```sh
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88 | npm install --save-dev babel-plugin-transform-function-bind
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89 | ```
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90 |
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91 | ## Usage
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92 |
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93 | ### Via `.babelrc` (Recommended)
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94 |
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95 | **.babelrc**
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96 |
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97 | ```json
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98 | {
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99 | "plugins": ["transform-function-bind"]
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100 | }
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101 | ```
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102 |
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103 | ### Via CLI
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104 |
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105 | ```sh
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106 | babel --plugins transform-function-bind script.js
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107 | ```
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108 |
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109 | ### Via Node API
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110 |
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111 | ```javascript
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112 | require("babel-core").transform("code", {
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113 | plugins: ["transform-function-bind"]
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114 | });
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115 | ```
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116 |
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117 | ## References
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118 |
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119 | * [Proposal](https://github.com/zenparsing/es-function-bind)
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120 | * [Babel Blog: Function Bind Syntax](/blog/2015/05/14/function-bind)
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