errors.md

Errors

Comma dangle

require trailing commas in multiline object literals

✅ Enabled (error)

// Bad
/*
var bad = {
	bar: 'baz',
	qux: 'quux'
};
*/

// Good
var good = {
	bar: 'baz',
	qux: 'quux',
};

No cond assign

disallow assignment in conditional expressions

✅ Enabled (error)

// Bad
/*
var x;
if (x = 0) {
	var b = 1;
}
*/

No console

disallow use of console

✅ Enabled (error)

// Bad
/*
console.log('hello world');
*/

No constant condition

disallow use of constant expressions in conditions

✅ Enabled (error)

// Bad
/*
if (false) {
	doSomethingUnfinished();
}
*/

No control regex

disallow control characters in regular expressions

✅ Enabled (error)

// Bad
/*
var pattern1 = /\x1f/;
var pattern2 = new RegExp('\x1f');
*/

// Good
var pattern1 = /\x20/;
var pattern2 = new RegExp('\x20');

No debugger

disallow use of debugger

✅ Enabled (error)

// Bad
/*
function isTruthy(x) {
	debugger;
	return Boolean(x);
}
*/

No dupe args

disallow duplicate arguments in functions

✅ Enabled (error)

// Bad
/*
function foo(a, b, a) {
	console.log('value of the second a:', a);
}
*/

No dupe keys

disallow duplicate keys when creating object literals

✅ Enabled (error)

// Bad
/*
var foo = {
	bar: 'baz',
	bar: 'qux'
};
*/

No duplicate case

disallow a duplicate case label.

✅ Enabled (error)

// Bad
/*
var a = 1;

switch (a) {
	case 1:
		break;
	case 2:
		break;
	case 1:
		break;
	default:
		break;
}
*/

No empty character class

disallow the use of empty character classes in regular expressions

✅ Enabled (error)

// Bad
/*
(/^abc[]/).test('abcdefg');
'abcdefg'.match(/^abc[]/);
*/

// Good
(/^abc/).test('abcdefg');
'abcdefg'.match(/^abc/);

No empty

disallow empty statements

✅ Enabled (error)

// Bad
/*
var foo = true;
if (foo) {

}
*/

No ex assign

disallow assigning to the exception in a catch block

✅ Enabled (error)

// Bad
/*
try {
	// code
} catch (e) {
	e = 10;
}
*/

No extra boolean cast

disallow double-negation boolean casts in a boolean context

❌ Disabled

No extra parens

disallow unnecessary parentheses

❌ Disabled

// Bad
var b = 1;
var c = 2;
var a = (b * c);
var d = (a * b) + c;

No extra semi

disallow unnecessary semicolons

✅ Enabled (error)

// Bad
/*
var x = 5;;
*/

No func assign

disallow overwriting functions written as function declarations

✅ Enabled (error)

// Bad
/*
function foo() {}
foo = bar;
*/

No inner declarations

disallow function or variable declarations in nested blocks

✅ Enabled (error)

// Bad
/*
if (test) {
	function doSomethingElse() { }
}
*/

// Good
function doSomething() { }

No invalid regexp

disallow invalid regular expression strings in the RegExp constructor

✅ Enabled (error)

// Bad
/*
RegExp('[');
RegExp('.', 'z');
new RegExp('\\');
*/

No irregular whitespace

disallow irregular whitespace outside of strings and comments

✅ Enabled (error)

No negated in lhs

disallow negation of the left operand of an in expression

✅ Enabled (error)

// Bad
/*
if (!key in object) {
	// operator precedence makes it equivalent to (!key) in object
	// and type conversion makes it equivalent to (key ? "false" : "true") in object
}
*/

No obj calls

disallow the use of object properties of the global object (Math and JSON) as functions

✅ Enabled (error)

// Bad
/*
var math = Math();
var json = JSON();
*/

No prototype builtins

disallow use of Object.prototypes builtins directly

✅ Enabled (error)

// Bad
/*
var hasBarProperty = foo.hasOwnProperty('bar');
var isPrototypeOfBar = foo.isPrototypeOf(bar);
var barIsEnumerable = foo.propertyIsEnumerable('bar');
*/

// Good
var hasBarProperty = {}.hasOwnProperty.call(foo, 'bar');
var isPrototypeOfBar = {}.isPrototypeOf.call(foo, bar);
var barIsEnumerable = {}.propertyIsEnumerable.call(foo, 'bar');

No regex spaces

disallow multiple spaces in a regular expression literal

✅ Enabled (error)

// Bad
/*
var re = /foo   bar/;
var re = new RegExp('foo   bar');
*/

// Good
var re = /foo {3}bar/;
var re = new RegExp('foo {3}bar');

No sparse arrays

disallow sparse arrays

✅ Enabled (error)

// Bad
/*
var items = [, ];
var colors = ['red',, 'blue'];
*/

// Good
var items = [];
var items = new Array(23);
var colors = ['red', 'blue'];

No unexpected multiline

Avoid code that looks like two expressions but is actually one

❌ Disabled

// Bad
let a = function () {}
`hello`

// Good
let b = function () {};
`hello`

No unreachable

disallow unreachable statements after a return, throw, continue, or break statement

✅ Enabled (error)

// Bad
/*
function foo() {
	return true;
	console.log('done');
}
*/

No unsafe finally

disallow return/throw/break/continue inside finally blocks

✅ Enabled (error)

// Bad
/*
let foo = function () {
	try {
		return 1;
	} catch (err) {
		return 2;
	} finally {
		return 3;
	}
};
*/

Use isnan

disallow comparisons with the value NaN

✅ Enabled (error)

// Bad
/*
if (foo === NaN) {
	// ...
}
*/

// Good
if (isNaN(foo)) {
	// ...
}

Valid jsdoc

ensure JSDoc comments are valid

✅ Enabled (error)

Valid typeof

ensure that the results of typeof are compared against a valid string

✅ Enabled (error)

// Bad
/*
typeof foo === 'strnig';
typeof foo === 'undefimed';
typeof bar !== 'nunber';
typeof bar !== 'fucntion';
*/

// Good
typeof foo === 'string';
typeof foo === 'undefined';
typeof bar !== 'number';
typeof bar !== 'function';