Package Exports

@babel/plugin-transform-for-of

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (@babel/plugin-transform-for-of) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

@babel/plugin-transform-for-of

Compile ES2015 for...of to ES5

Example

for (var i of foo) {}

Out

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

npm install --save-dev @babel/plugin-transform-for-of

Usage

Via `.babelrc` (Recommended)

.babelrc

Without options:

{
  "plugins": ["@babel/plugin-transform-for-of"]
}

With options:

{
  "plugins": [
    ["@babel/plugin-transform-for-of", {
      "loose": true, // defaults to false
      "assumeArray": true // defaults to false
    }]
  ]
}

Via CLI

babel --plugins @babel/plugin-transform-for-of script.js

Via Node API

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

for (var i of foo) {}

Out

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 and babel/babel#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.

for (let a of [1,2,3]) {}

Out

var _arr = [1, 2, 3];
for (var _i = 0; _i < _arr.length; _i++) {
  var a = _arr[_i];
}