Eslint-plugin-no-for-each NPM

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

You'll first need to install ESLint:

$ 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

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

{
  "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

"rules": {
  "...": "...",
  "no-for-each/cache-for-length": 2,
  "no-excessive-blank-lines": 2
}

Resources

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
truncating body at some point

jsperf

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