docs/src/rules/logical-assignment-operators.md
ES2021 introduces the assignment operator shorthand for the logical operators ||, && and ??.
Before, this was only allowed for mathematical operations such as + or * (see the rule operator-assignment).
The shorthand can be used if the assignment target and the left expression of a logical expression are the same.
For example a = a || b can be shortened to a ||= b.
This rule requires or disallows logical assignment operator shorthand.
This rule has a string and an object option. String option:
"always" (default)"never"Object option (only available if string option is set to "always"):
"enforceForIfStatements": false (default) Do not check for equivalent if statements."enforceForIfStatements": true Check for equivalent if statements.This option checks for expressions that can be shortened using logical assignment operator. For example, a = a || b can be shortened to a ||= b.
Expressions with associativity such as a = a || b || c are reported as being able to be shortened to a ||= b || c unless the evaluation order is explicitly defined using parentheses, such as a = (a || b) || c.
Examples of incorrect code for this rule with the default "always" option:
::: incorrect
/*eslint logical-assignment-operators: ["error", "always"]*/
a = a || b
a = a && b
a = a ?? b
a || (a = b)
a && (a = b)
a ?? (a = b)
a = a || b || c
a = a && b && c
a = a ?? b ?? c
:::
Examples of correct code for this rule with the default "always" option:
::: correct
/*eslint logical-assignment-operators: ["error", "always"]*/
a = b
a += b
a ||= b
a = b || c
a || (b = c)
if (a) a = b
a = (a || b) || c
:::
Examples of incorrect code for this rule with the "never" option:
::: incorrect
/*eslint logical-assignment-operators: ["error", "never"]*/
a ||= b
a &&= b
a ??= b
:::
Examples of correct code for this rule with the "never" option:
::: correct
/*eslint logical-assignment-operators: ["error", "never"]*/
a = a || b
a = a && b
a = a ?? b
:::
This option checks for additional patterns with if statements which could be expressed with the logical assignment operator.
Examples of incorrect code for this rule with the ["always", { enforceForIfStatements: true }] option:
::: incorrect
/*eslint logical-assignment-operators: ["error", "always", { enforceForIfStatements: true }]*/
if (a) a = b // <=> a &&= b
if (!a) a = b // <=> a ||= b
if (a == null) a = b // <=> a ??= b
if (a === null || a === undefined) a = b // <=> a ??= b
:::
Examples of correct code for this rule with the ["always", { enforceForIfStatements: true }] option:
::: correct
/*eslint logical-assignment-operators: ["error", "always", { enforceForIfStatements: true }]*/
if (a) b = c
if (a === 0) a = b
:::
Use of logical operator assignment shorthand is a stylistic choice. Leaving this rule turned off would allow developers to choose which style is more readable on a case-by-case basis.