In
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) {
_iterator.return();
}
} finally {
if (_didIteratorError) {
throw _iteratorError;
}
}
}
npm install --save-dev babel-plugin-transform-es2015-for-of
.babelrc (Recommended).babelrc
Without options:
{
"plugins": ["transform-es2015-for-of"]
}
With options:
{
"plugins": [
["transform-es2015-for-of", {
"loose": true
}]
]
}
babel --plugins transform-es2015-for-of script.js
require("babel-core").transform("code", {
plugins: ["transform-es2015-for-of"]
});
looseboolean, 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.
In
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;
}
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.
If a basic array is used, Babel will compile the for-of loop down to a regular for loop.
In
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];
}