Require === and !== (eqeqeq)

It is considered good practice to use the type-safe equality operators === and !== instead of their regular counterparts == and !=.

The reason for this is that == and != do type coercion which follows the rather obscure Abstract Equality Comparison Algorithm. For instance, the following statements are all considered true:

• [] == false
• [] == ![]
• 3 == "03"

If one of those occurs in an innocent-looking statement such as a == b the actual problem is very difficult to spot.

Rule Details

This rule is aimed at eliminating the type-unsafe equality operators.

Examples of incorrect code for this rule:

/*eslint eqeqeq: "error"*/

if (x == 42) { }

if ("" == text) { }

if (obj.getStuff() != undefined) { }

The --fix option on the command line automatically fixes some problems reported by this rule. A problem is only fixed if one of the operands is a typeof expression, or if both operands are literals with the same type.

Options

always

The "always" option (default) enforces the use of === and !== in every situation (except when you opt-in to more specific handling of null [see below]).

Examples of incorrect code for the "always" option:

/*eslint eqeqeq: ["error", "always"]*/

a == b
foo == true
bananas != 1
value == undefined
typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null

Examples of correct code for the "always" option:

/*eslint eqeqeq: ["error", "always"]*/

a === b
foo === true
bananas !== 1
value === undefined
typeof foo === 'undefined'
'hello' !== 'world'
0 === 0
true === true
foo === null

This rule optionally takes a second argument, which should be an object with the following supported properties:

• "null": Customize how this rule treats null literals. Possible values:
  • always (default) - Always use === or !==.
  • never - Never use === or !== with null.
  • ignore - Do not apply this rule to null.

smart

The "smart" option enforces the use of === and !== except for these cases:

• Comparing two literal values
• Evaluating the value of typeof
• Comparing against null

Examples of incorrect code for the "smart" option:

/*eslint eqeqeq: ["error", "smart"]*/

// comparing two variables requires ===
a == b

// only one side is a literal
foo == true
bananas != 1

// comparing to undefined requires ===
value == undefined

Examples of correct code for the "smart" option:

/*eslint eqeqeq: ["error", "smart"]*/

typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null

allow-null

Deprecated: Instead of using this option use "always" and pass a "null" option property with value "ignore". This will tell eslint to always enforce strict equality except when comparing with the null literal.

["error", "always", {"null": "ignore"}]

When Not To Use It

If you don't want to enforce a style for using equality operators, then it's safe to disable this rule. Source: http://eslint.org/docs/rules/

Disallow Use of Alert (no-alert)

JavaScript's alert, confirm, and prompt functions are widely considered to be obtrusive as UI elements and should be replaced by a more appropriate custom UI implementation. Furthermore, alert is often used while debugging code, which should be removed before deployment to production.

alert("here!");

Rule Details

This rule is aimed at catching debugging code that should be removed and popup UI elements that should be replaced with less obtrusive, custom UIs. As such, it will warn when it encounters alert, prompt, and confirm function calls which are not shadowed.

Examples of incorrect code for this rule:

/*eslint no-alert: "error"*/

alert("here!");

confirm("Are you sure?");

prompt("What's your name?", "John Doe");

Examples of correct code for this rule:

/*eslint no-alert: "error"*/

customAlert("Something happened!");

customConfirm("Are you sure?");

customPrompt("Who are you?");

function foo() {
    var alert = myCustomLib.customAlert;
    alert();
}

Related Rules

• [no-console](no-console.md)
• [no-debugger](no-debugger.md) Source: http://eslint.org/docs/rules/

For more information visit Source: http://eslint.org/docs/rules/

Checks that operators have space around them, except for ** which should not have surrounding space.

Example:

# bad
total = 3*4
"apple"+"juice"
my_number = 38/4
a ** b

# good
total = 3 * 4
"apple" + "juice"
my_number = 38 / 4
a**b

This cop makes sure that predicates are named properly.

Example:

# bad
def is_even?(value)
end

# good
def even?(value)
end

# bad
def has_value?
end

# good
def value?
end

Check that the keys, separators, and values of a multi-line hash literal are aligned according to configuration. The configuration options are:

- key (left align keys)
- separator (align hash rockets and colons, right align keys)
- table (left align keys, hash rockets, and values)

The treatment of hashes passed as the last argument to a method call can also be configured. The options are:

- always_inspect
- always_ignore
- ignore_implicit (without curly braces)
- ignore_explicit (with curly braces)

Example:

# EnforcedHashRocketStyle: key (default)
# EnforcedColonStyle: key (default)

# good
{
  foo: bar,
  ba: baz
}
{
  :foo => bar,
  :ba => baz
}

# bad
{
  foo: bar,
   ba: baz
}
{
  :foo => bar,
   :ba => baz
}

Example:

# EnforcedHashRocketStyle: separator
# EnforcedColonStyle: separator

#good
{
  foo: bar,
   ba: baz
}
{
  :foo => bar,
   :ba => baz
}

#bad
{
  foo: bar,
  ba: baz
}
{
  :foo => bar,
  :ba => baz
}
{
  :foo => bar,
  :ba  => baz
}

Example:

# EnforcedHashRocketStyle: table
# EnforcedColonStyle: table

#good
{
  foo: bar,
  ba:  baz
}
{
  :foo => bar,
  :ba  => baz
}

#bad
{
  foo: bar,
  ba: baz
}
{
  :foo => bar,
   :ba => baz
}

Check that the keys, separators, and values of a multi-line hash literal are aligned according to configuration. The configuration options are:

- key (left align keys)
- separator (align hash rockets and colons, right align keys)
- table (left align keys, hash rockets, and values)

The treatment of hashes passed as the last argument to a method call can also be configured. The options are:

- always_inspect
- always_ignore
- ignore_implicit (without curly braces)
- ignore_explicit (with curly braces)

Example:

# EnforcedHashRocketStyle: key (default)
# EnforcedColonStyle: key (default)

# good
{
  foo: bar,
  ba: baz
}
{
  :foo => bar,
  :ba => baz
}

# bad
{
  foo: bar,
   ba: baz
}
{
  :foo => bar,
   :ba => baz
}

Example:

# EnforcedHashRocketStyle: separator
# EnforcedColonStyle: separator

#good
{
  foo: bar,
   ba: baz
}
{
  :foo => bar,
   :ba => baz
}

#bad
{
  foo: bar,
  ba: baz
}
{
  :foo => bar,
  :ba => baz
}
{
  :foo => bar,
  :ba  => baz
}

Example:

# EnforcedHashRocketStyle: table
# EnforcedColonStyle: table

#good
{
  foo: bar,
  ba:  baz
}
{
  :foo => bar,
  :ba  => baz
}

#bad
{
  foo: bar,
  ba: baz
}
{
  :foo => bar,
   :ba => baz
}

Check that the keys, separators, and values of a multi-line hash literal are aligned according to configuration. The configuration options are:

- key (left align keys)
- separator (align hash rockets and colons, right align keys)
- table (left align keys, hash rockets, and values)

The treatment of hashes passed as the last argument to a method call can also be configured. The options are:

- always_inspect
- always_ignore
- ignore_implicit (without curly braces)
- ignore_explicit (with curly braces)

Example:

# EnforcedHashRocketStyle: key (default)
# EnforcedColonStyle: key (default)

# good
{
  foo: bar,
  ba: baz
}
{
  :foo => bar,
  :ba => baz
}

# bad
{
  foo: bar,
   ba: baz
}
{
  :foo => bar,
   :ba => baz
}

Example:

# EnforcedHashRocketStyle: separator
# EnforcedColonStyle: separator

#good
{
  foo: bar,
   ba: baz
}
{
  :foo => bar,
   :ba => baz
}

#bad
{
  foo: bar,
  ba: baz
}
{
  :foo => bar,
  :ba => baz
}
{
  :foo => bar,
  :ba  => baz
}

Example:

# EnforcedHashRocketStyle: table
# EnforcedColonStyle: table

#good
{
  foo: bar,
  ba:  baz
}
{
  :foo => bar,
  :ba  => baz
}

#bad
{
  foo: bar,
  ba: baz
}
{
  :foo => bar,
   :ba => baz
}

This cops checks if empty lines exist around the bodies of methods.

Example:

# good

def foo
  # ...
end

# bad

def bar

  # ...

end

This cop checks whether method definitions are separated by one empty line.

NumberOfEmptyLines can be and integer (e.g. 1 by default) or an array (e.g. [1, 2]) to specificy a minimum and a maximum of empty lines.

AllowAdjacentOneLineDefs can be used to configure is adjacent one line methods definitions are an offense

Example:

# bad
def a
end
def b
end

Example:

# good
def a
end

def b
end

For more information visit Source: http://eslint.org/docs/rules/

For more information visit Source: http://eslint.org/docs/rules/

Use next to skip iteration instead of a condition at the end.

Example: EnforcedStyle: skipmodifierifs (default)

# bad
[1, 2].each do |a|
  if a == 1
    puts a
  end
end

# good
[1, 2].each do |a|
  next unless a == 1
  puts a
end

# good
[1, 2].each do |o|
  puts o unless o == 1
end

Example: EnforcedStyle: always

# With `always` all conditions at the end of an iteration needs to be
# replaced by next - with `skip_modifier_ifs` the modifier if like
# this one are ignored: `[1, 2].each { |a| return 'yes' if a == 1 }`

# bad
[1, 2].each do |o|
  puts o unless o == 1
end

# bad
[1, 2].each do |a|
  if a == 1
    puts a
  end
end

# good
[1, 2].each do |a|
  next unless a == 1
  puts a
end

This cop checks for redundant return expressions.

Example:

def test
  return something
end

def test
  one
  two
  three
  return something
end

It should be extended to handle methods whose body is if/else or a case expression with a default branch.

Check that the keys, separators, and values of a multi-line hash literal are aligned according to configuration. The configuration options are:

- key (left align keys)
- separator (align hash rockets and colons, right align keys)
- table (left align keys, hash rockets, and values)

The treatment of hashes passed as the last argument to a method call can also be configured. The options are:

- always_inspect
- always_ignore
- ignore_implicit (without curly braces)
- ignore_explicit (with curly braces)

Example:

# EnforcedHashRocketStyle: key (default)
# EnforcedColonStyle: key (default)

# good
{
  foo: bar,
  ba: baz
}
{
  :foo => bar,
  :ba => baz
}

# bad
{
  foo: bar,
   ba: baz
}
{
  :foo => bar,
   :ba => baz
}

Example:

# EnforcedHashRocketStyle: separator
# EnforcedColonStyle: separator

#good
{
  foo: bar,
   ba: baz
}
{
  :foo => bar,
   :ba => baz
}

#bad
{
  foo: bar,
  ba: baz
}
{
  :foo => bar,
  :ba => baz
}
{
  :foo => bar,
  :ba  => baz
}

Example:

# EnforcedHashRocketStyle: table
# EnforcedColonStyle: table

#good
{
  foo: bar,
  ba:  baz
}
{
  :foo => bar,
  :ba  => baz
}

#bad
{
  foo: bar,
  ba: baz
}
{
  :foo => bar,
   :ba => baz
}

This cop makes sure that all variables use the configured style, snake_case or camelCase, for their names.

Example: EnforcedStyle: snake_case (default)

# bad
fooBar = 1

# good
foo_bar = 1

Example: EnforcedStyle: camelCase

# bad
foo_bar = 1

# good
fooBar = 1

This cop checks hash literal syntax.

It can enforce either the use of the class hash rocket syntax or the use of the newer Ruby 1.9 syntax (when applicable).

A separate offense is registered for each problematic pair.

The supported styles are:

• ruby19 - forces use of the 1.9 syntax (e.g. {a: 1}) when hashes have all symbols for keys
• hash_rockets - forces use of hash rockets for all hashes
• nomixedkeys - simply checks for hashes with mixed syntaxes
• ruby19nomixed_keys - forces use of ruby 1.9 syntax and forbids mixed syntax hashes

Example: EnforcedStyle: ruby19 (default)

# bad
{:a => 2}
{b: 1, :c => 2}

# good
{a: 2, b: 1}
{:c => 2, 'd' => 2} # acceptable since 'd' isn't a symbol
{d: 1, 'e' => 2} # technically not forbidden

Example: EnforcedStyle: hash_rockets

# bad
{a: 1, b: 2}
{c: 1, 'd' => 5}

# good
{:a => 1, :b => 2}

Example: EnforcedStyle: nomixedkeys

# bad
{:a => 1, b: 2}
{c: 1, 'd' => 2}

# good
{:a => 1, :b => 2}
{c: 1, d: 2}

Example: EnforcedStyle: ruby19nomixed_keys

# bad
{:a => 1, :b => 2}
{c: 2, 'd' => 3} # should just use hash rockets

# good
{a: 1, b: 2}
{:c => 3, 'd' => 4}