| 1 | # babel-plugin-transform-es2015-for-of
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| 2 |
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| 3 | > Compile ES2015 for...of to ES5
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| 4 |
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| 5 | ## Example
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| 6 |
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| 7 | **In**
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| 8 |
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| 9 | ```js
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| 10 | for (var i of foo) {}
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| 11 | ```
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| 12 |
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| 13 | **Out**
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| 14 |
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| 15 | ```js
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| 16 | var _iteratorNormalCompletion = true;
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| 17 | var _didIteratorError = false;
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| 18 | var _iteratorError = undefined;
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| 19 |
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| 20 | try {
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| 21 | for (var _iterator = foo[Symbol.iterator](), _step; !(_iteratorNormalCompletion = (_step = _iterator.next()).done); _iteratorNormalCompletion = true) {
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| 22 | var i = _step.value;
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| 23 | }
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| 24 | } catch (err) {
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| 25 | _didIteratorError = true;
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| 26 | _iteratorError = err;
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| 27 | } finally {
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| 28 | try {
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| 29 | if (!_iteratorNormalCompletion && _iterator.return) {
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| 30 | _iterator.return();
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| 31 | }
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| 32 | } finally {
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| 33 | if (_didIteratorError) {
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| 34 | throw _iteratorError;
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| 35 | }
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| 36 | }
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| 37 | }
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| 38 | ```
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| 39 |
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| 40 | ## Installation
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| 41 |
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| 42 | ```sh
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| 43 | npm install --save-dev babel-plugin-transform-es2015-for-of
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| 44 | ```
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| 45 |
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| 46 | ## Usage
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| 47 |
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| 48 | ### Via `.babelrc` (Recommended)
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| 49 |
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| 50 | **.babelrc**
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| 51 |
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| 52 | ```js
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| 53 | // without options
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| 54 | {
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| 55 | "plugins": ["transform-es2015-for-of"]
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| 56 | }
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| 57 |
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| 58 | // with options
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| 59 | {
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| 60 | "plugins": [
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| 61 | ["transform-es2015-for-of", {
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| 62 | "loose": true
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| 63 | }]
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| 64 | ]
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| 65 | }
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| 66 | ```
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| 67 |
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| 68 | ### Via CLI
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| 69 |
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| 70 | ```sh
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| 71 | babel --plugins transform-es2015-for-of script.js
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| 72 | ```
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| 73 |
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| 74 | ### Via Node API
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| 75 |
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| 76 | ```javascript
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| 77 | require("babel-core").transform("code", {
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| 78 | plugins: ["transform-es2015-for-of"]
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| 79 | });
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| 80 | ```
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| 81 |
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| 82 | ## Options
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| 83 |
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| 84 | ### `loose`
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| 85 |
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| 86 | `boolean`, defaults to `false`
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| 87 |
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| 88 | In loose mode, arrays are put in a fast path, thus heavily increasing performance.
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| 89 | All other iterables will continue to work fine.
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| 90 |
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| 91 | #### Example
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| 92 |
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| 93 | **In**
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| 94 |
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| 95 | ```js
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| 96 | for (var i of foo) {}
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| 97 | ```
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| 98 |
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| 99 | **Out**
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| 100 |
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| 101 | ```js
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| 102 | for (var _iterator = foo, _isArray = Array.isArray(_iterator), _i = 0, _iterator = _isArray ? _iterator : _iterator[Symbol.iterator]();;) {
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| 103 | var _ref;
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| 104 |
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| 105 | if (_isArray) {
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| 106 | if (_i >= _iterator.length) break;
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| 107 | _ref = _iterator[_i++];
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| 108 | } else {
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| 109 | _i = _iterator.next();
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| 110 | if (_i.done) break;
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| 111 | _ref = _i.value;
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| 112 | }
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| 113 |
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| 114 | var i = _ref;
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| 115 | }
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| 116 | ```
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| 117 |
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| 118 | #### Abrupt completions
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| 119 |
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| 120 | In loose mode an iterator's `return` method will not be called on abrupt completions caused by thrown errors.
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| 121 |
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| 122 | Please see [google/traceur-compiler#1773](https://github.com/google/traceur-compiler/issues/1773) and
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| 123 | [babel/babel#838](https://github.com/babel/babel/issues/838) for more information.
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| 124 |
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| 125 | ### Optimization
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| 126 |
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| 127 | If a basic array is used, Babel will compile the for-of loop down to a regular for loop.
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| 128 |
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| 129 | **In**
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| 130 |
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| 131 | ```js
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| 132 | for (let a of [1,2,3]) {}
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| 133 | ```
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| 134 |
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| 135 | **Out**
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| 136 |
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| 137 | ```js
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| 138 | var _arr = [1, 2, 3];
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| 139 | for (var _i = 0; _i < _arr.length; _i++) {
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| 140 | var a = _arr[_i];
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| 141 | }
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| 142 | ```
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