Logical AND assignment (&&=) - JavaScript 编辑

The logical AND assignment (x &&= y) operator only assigns if x is truthy.

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The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

Syntax

expr1 &&= expr2

Description

Short-circuit evaluation

The logical AND operator is evaluated left to right, it is tested for possible short-circuit evaluation using the following rule:

(some falsy expression) && expr is short-circuit evaluated to the falsy expression;

Short circuit means that the expr part above is not evaluated, hence any side effects of doing so do not take effect (e.g., if expr is a function call, the calling never takes place).

Logical AND assignment short-circuits as well meaning that x &&= y is equivalent to:

x && (x = y);

And not equivalent to the following which would always perform an assignment:

x = x && y;

Examples

Using logical AND assignment

let x = 0;
let y = 1;

x &&= 0; // 0
x &&= 1; // 0
y &&= 1; // 1
y &&= 0; // 0

Specifications

Specification
Logical Assignment Operators The definition of 'Assignment operators' in that specification.

Browser compatibility

BCD tables only load in the browser

See also

• Logical AND (&&)
• The nullish coalescing operator (??)
• Bitwise AND assignment (&=)
• Boolean
• Truthy
• Falsy