eslint-config-chain-able
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an opinionated ESLint configuration
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# eslint-plugin-no-for-each
What it does? Fix `forEach`, `for in`, and `for of` loops.
Before:
After:
`['error', 'cache-length']`
`['error']`
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