# eslint-plugin-no-for-each
What it does? Fix `forEach`, `for in`, and `for of` loops.

Before:

![image](https://cloud.githubusercontent.com/assets/4022631/20047084/8ed348e0-a465-11e6-90f4-4715f5498699.png)

After:

`['error', 'cache-length']`
![image](https://cloud.githubusercontent.com/assets/4022631/20047228/fa5ed9fc-a466-11e6-87b6-f490be782748.png)

`['error']`
![image](https://cloud.githubusercontent.com/assets/4022631/20047232/ffab29a6-a466-11e6-8dcf-436c40d97757.png)

https://jsperf.com/foreach-vs-for-loop-vs-for-in-vs-for-of-vs-babel-for-of

## [Installation](#installation)

You'll first need to install [ESLint](http://eslint.org):

```
$ npm i eslint --save-dev
```

Next, install `eslint-plugin-no-for-each`:

```
$ npm install eslint-plugin-no-for-each --save-dev
```

**Note:** If you installed ESLint globally (using the `-g` flag) then you must also install `eslint-plugin-no-for-each` globally.

## [Configuration](#configuration)
Add `no-for-each` to the plugins section of your `.eslintrc` configuration file.
Then configure the rules you want to use under the rules section.

- default: `1` or `["error"]`
- cache-length: `2`

```json
{
  "plugins": [
    "no-for-each"
  ],
  "rules": {
    "no-for-each/no-for-each": 2,
    "no-for-each/no-for-of": 2,
    "no-for-each/no-for-in": 2,
  }
}
```

## two additional WIP rules
```json
"rules": {
  "...": "...",
  "no-for-each/cache-for-length": 2,
  "no-excessive-blank-lines": 2
}
```

# Resources
- https://www.kenneth-truyers.net/2016/05/27/writing-custom-eslint-rules/
- https://github.com/airbnb/javascript/issues/851
- https://insideops.wordpress.com/2015/12/08/creating-custom-rules-for-eslint/
- https://medium.com/tumblbug-engineering/creating-an-eslint-plugin-87f1cb42767f#.z5t30ge87
- http://stackoverflow.com/questions/34130718/how-to-create-customized-eslint-rules/34186003
- http://stackoverflow.com/questions/38278273/eslint-code-vs-whitespace-values-for-fixable
- https://github.com/eslint/eslint/commit/a9a4652b2ce92858d90243e7bb8693f458a14783
- https://github.com/facebookincubator/create-react-app/issues/272
- https://github.com/facebookincubator/create-react-app/issues/274
- https://github.com/yannickcr/eslint-plugin-react/blob/master/lib/rules/jsx-equals-spacing.js#L18
- https://github.com/jfmengels/eslint-rule-documentation/blob/master/contributing.md
- https://github.com/Gillespie59/eslint-plugin-angular
- http://eslint.org/docs/developer-guide/working-with-rules
- http://eslint.org/blog/2016/07/eslint-new-rule-format
- http://eslint.org/docs/developer-guide/working-with-rules-new
- https://github.com/buildo/eslint-plugin-no-loops (had no fixing, was no loops in general)
- https://github.com/airbnb/javascript#iterators--nope
- https://www.paypal-engineering.com/2014/12/12/maintaining-javascript-code-quality-with-eslint/
- https://babeljs.io/repl/
- http://eslint.org/docs/rules/

# known bugs
- [ ] properly parse `Object.keys(apples).forEach(apple => delete apples[apple])` because it replaces `apple` with new var, but not `apples` so it leaves the `s`
- [ ] nested loops, will do this soon
- [x] truncating body at some point

# jsperf
```javascript
var testData = [];
for (var i = 0; i < 100; i++) {
  testData.push(i);
}

// forEach
var res = 0;
testData.forEach(function(x) {
  res += x;
});

// for
var res = 0;
for (var i = 0; i < testData.length; i++) {
  res += testData[i];
}

// for optimized
var res = 0;
for (var i = 0, len = testData.length; i < len; i++) {
  res += testData[i];
}

// reduce
var res = testData.reduce(function(sum, x) {
  return sum + x;
}, 0);


// while
var res = 0;
var i = testData.length;
while (i--) {
    res += testData[i];
}

// for in
var res = 0;
for (var data in testData) {
  res += testData[i];
}


// for of
var res = 0;
for (var data of testData) {
  res += testData[i];
}


// for of babel
var res = 0;
var _iteratorNormalCompletion = true;
var _didIteratorError = false;
var _iteratorError = undefined;

try {
  for (var _iterator = testData[Symbol.iterator](), _step; !(_iteratorNormalCompletion = (_step = _iterator.next()).done); _iteratorNormalCompletion = true) {
    var value = _step.value;

    console.log(value);
  }
} catch (err) {
  _didIteratorError = true;
  _iteratorError = err;
} finally {
  try {
    res += testData[i];
    if (!_iteratorNormalCompletion && _iterator.return) {
      _iterator.return();
    }
  } finally {
    if (_didIteratorError) {
      throw _iteratorError;
    }
  }
}
```


# @NOTES:
---
could keep option `cache-length`
but since we are using an object,
seems silly to call object.keys 2x
---
we do not use body.body because
- 1) not always there
- 2) we want to keep curly braces (or lack of from the source
----

(when it has proper configs and has large files to test, then release 1.0.0)
# @TODO:
- [ ] add config option for `cache-length-inside-loop` (var i = 0, len = varName.length; ...)
- [ ] recommend let => const rule
- [ ] add large js files to test failed fixing & safety
- [ ] isDev | isTest helper funcs
- [ ] ^ add args in tests for `devtest`
- [ ] comment on readmes
- [ ] move todos to issues
- [ ] use type in the `left` of the loop such as `const`, `let`, `var`
- [ ] o.hasOwnProperty for for in/of
- [ ] (lower priority) make a guide how to make an eslint plugin