Require the use of ===
and !==
Some problems reported by this rule are automatically fixable by the --fix
command line option
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.
This rule is aimed at eliminating the type-unsafe equality operators.
Examples of incorrect code for this rule:
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.
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:
Examples of correct code for the "always"
option:
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
.The "smart"
option enforces the use of ===
and !==
except for these cases:
typeof
null
Examples of incorrect code for the "smart"
option:
Examples of correct code for the "smart"
option:
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.
If you don’t want to enforce a style for using equality operators, then it’s safe to disable this rule.
This rule was introduced in ESLint v0.0.2.
© OpenJS Foundation and other contributors
Licensed under the MIT License.
https://eslint.org/docs/latest/rules/eqeqeq