logical-assignment-operators - ESLint - Pluggable JavaScript Linter (original) (raw)

Require or disallow logical assignment operator shorthand

🔧 Fixable

Some problems reported by this rule are automatically fixable by the --fix command line option

💡 hasSuggestions

Some problems reported by this rule are manually fixable by editor suggestions

❄️ Frozen

This rule is currently frozen and is not accepting feature requests.

Table of Contents

  1. Rule Details
    1. Options
      1. always
      2. never
      3. enforceForIfStatements
  2. When Not To Use It
  3. Version
  4. Resources

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:

Object option (only available if string option is set to "always"):

always

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:

Open in Playground

/*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:

Open in Playground

/*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

never

Examples of incorrect code for this rule with the "never" option:

Open in Playground

/*eslint logical-assignment-operators: ["error", "never"]*/

a ||= b
a &&= b
a ??= b

Examples of correct code for this rule with the "never" option:

Open in Playground

/*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.

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

Open in Playground

/*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:

Open in Playground

/*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.

Version

This rule was introduced in ESLint v8.24.0.

Resources