logical-assignment-operators.md

title	layout	rule_type
logical-assignment-operators	doc	suggestion

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.

Rule Details

This rule requires or disallows logical assignment operator shorthand.

Options

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

always

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)

:::

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

:::

never

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

:::

enforceForIfStatements

This option checks for additional patterns with if statements which could be expressed with the logical assignment operator.

::: incorrect

Examples of incorrect code for this rule with the ["always", { enforceIfStatements: true }] option:

/*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", { enforceIfStatements: true }] option:

::: correct

/*eslint logical-assignment-operators: ["error", "always", { enforceForIfStatements: true }]*/

if (a) b = c
if (a === 0) a = b

:::

When Not To Use It

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.