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ESLint Genius

An ESLint config for geniuses.

But you can continue to be standard if you want.

This is a combination of best practices, styles that have objective benefits, and my own (let's face it, correct) opinions. I try to provide my rationale for the more contentious decisions.

Base config

{
  "extends": "eslint:recommended",
  "parserOptions": {
    "ecmaVersion": 6,
    "sourceType": "module"
  }
}
"error"

Require camelCase for variables and object properties.

[
  "error",
  "always-multiline"
]

Require multiline list items to have a dangling comma.

  • Makes adding and reordering items a whole lot less fiddly.
  • Simplifies diffs and makes them clearer. See the ESLint documentation for a good example of this.

Wrong

const things = [
	'foo',
	'bar'
];

const data = {
	foo: 'bar',
	baz: 'bat'
}

Right

const things = [
	'foo',
	'bar',
];

const data = {
	foo: 'bar',
	baz: 'bat',
};
"error"

Space after commas, but not before.

"error"

Require a comma after and on the same line as an array element, object property, or variable declaration

"error"

Blocks require curly braces.

  • More consistent.
  • Easier and less error-prone to refactor a block later to include more lines.

Wrong

if (foo) alert(foo);

if (foo)
	alert(foo);
	alert(bar); // not inside the if block!

Right

if (foo) {
	alert(foo);
}

if (foo) {
	alert(foo);
}
alert(bar); // obviously not inside the if block.
"error"

Require a newline at the end of files.

"error"

Always require === and !==, even for literals on both sides and even when null is involved.

[
  "error",
  "never"
]

Disallow whitespace between a function call and its parens.

[
  "error",
  "smart-tabs"
]

Require tabs for indentation, but spaces for alignment. Combining them in this specific way provides the best of both.

  • Tabs maintain their intended purpose of indentation, and nothing else.
  • Code can always be viewed using the tab width the reader is most comfortable with.
  • Lined-up code will stay lined-up no matter what.

Wrong

if (foo) {
/*ss*/alert(foo);
}

const data = {
/*tab*/foo: 'barbaz',/*tab*/ // Some descriptive text
/*tab*//*tab*//*tab*//*tab*/ // explaining this item
/*tab*/quz: 'qux',
};

Right

if (foo) {
/*tab*/alert(foo);
}

const data = {
/*tab*/foo: 'barbaz', // Some descriptive text
/*tab*//*ssssssssss*/ // explaining this item
/*tab*/quz: 'qux',
};
"error"

Do not allow trailing whitespace, even on blank lines.

"error"

Always require let or const as opposed to var.

"error"

Always prefer const as opposed to let when possible.

"error"

Always require semicolons.

"error"

Require a space before the opening brace of a block.

Wrong

if (a){
	b();
}

function a(){}

try {} catch(a){}

class Foo{
	constructor(){}
}

Right

if (a) {
	b();
}

function a() {}

try {} catch(a) {}

class Foo {
	constructor() {}
}
[
  "error",
  {
    "anonymous": "always",
    "named": "never",
    "asyncArrow": "always"
  }
]

Require a space after anonymous and arrow function parens and disallow for named function parens.

[
  "error",
  "never"
]

Disallow spaces padding the insides of parens.

[
  "error",
  {
    "words": true,
    "nonwords": false,
    "overrides": {
      "!": true,
      "!!": true
    }
  }
]

Require a space after ! and !!, but not other non-word unary operators.

  • It can be very easy to miss a ! (and, to a lesser extent, !!) in front of a variable when scanning code. A space instantly makes things clearer at a glance.
  • Other unary operators are much easier to see.

Wrong

if (!foo) {
	badFooCount ++;
}

foo = !bar;

Right

if (! foo) {
	badFooCount++;
}

foo = ! bar;

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