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# @babel/plugin-transform-for-of
> Compile ES2015 for...of to ES5
## Example
**In**
```js
for (var i of foo) {}
```
**Out**
```js
var _iteratorNormalCompletion = true;
var _didIteratorError = false;
var _iteratorError = undefined;
try {
for (var _iterator = foo[Symbol.iterator](), _step; !(_iteratorNormalCompletion = (_step = _iterator.next()).done); _iteratorNormalCompletion = true) {
var i = _step.value;
}
} catch (err) {
_didIteratorError = true;
_iteratorError = err;
} finally {
try {
if (!_iteratorNormalCompletion && _iterator.return != null) {
_iterator.return();
}
} finally {
if (_didIteratorError) {
throw _iteratorError;
}
}
}
```
## Installation
```sh
npm install --save-dev @babel/plugin-transform-for-of
```
## Usage
### Via `.babelrc` (Recommended)
**.babelrc**
Without options:
```js
{
"plugins": ["@babel/plugin-transform-for-of"]
}
```
With options:
```js
{
"plugins": [
["@babel/plugin-transform-for-of", {
"loose": true, // defaults to false
"assumeArray": true // defaults to false
}]
]
}
```
### Via CLI
```sh
babel --plugins @babel/plugin-transform-for-of script.js
```
### Via Node API
```javascript
require("@babel/core").transform("code", {
plugins: ["@babel/plugin-transform-for-of"]
});
```
## Options
### `loose`
`boolean`, defaults to `false`
In loose mode, arrays are put in a fast path, thus heavily increasing performance.
All other iterables will continue to work fine.
#### Example
**In**
```js
for (var i of foo) {}
```
**Out**
```js
for (var _iterator = foo, _isArray = Array.isArray(_iterator), _i = 0, _iterator = _isArray ? _iterator : _iterator[Symbol.iterator]();;) {
var _ref;
if (_isArray) {
if (_i >= _iterator.length) break;
_ref = _iterator[_i++];
} else {
_i = _iterator.next();
if (_i.done) break;
_ref = _i.value;
}
var i = _ref;
}
```
#### Abrupt completions
In loose mode an iterator's `return` method will not be called on abrupt completions caused by thrown errors.
Please see [google/traceur-compiler#1773](https://github.com/google/traceur-compiler/issues/1773) and
[babel/babel#838](https://github.com/babel/babel/issues/838) for more information.
### `assumeArray`
`boolean`, defaults to `false`
This will apply the optimization shown below to all for-of loops by assuming that _all_ loops are arrays.
Can be useful when you just want a for-of loop to represent a basic for loop over an array.
### Optimization
If a basic array is used, Babel will compile the for-of loop down to a regular for loop.
**In**
```js
for (let a of [1,2,3]) {}
```
**Out**
```js
var _arr = [1, 2, 3];
for (var _i = 0; _i < _arr.length; _i++) {
var a = _arr[_i];
}
```
|
