Logical AND assignment (&&=)

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

语法

expr1 &&= expr2

描述

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;

例子

Using logical AND assignment

let x = 0;
let y = 1;

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

规范

Specification
Logical Assignment Operators
Assignment operators

浏览器兼容性

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Logical AND assignment (x &&= y)Chrome Full support 85Edge Full support 85Firefox Full support 79IE No support NoOpera No support NoSafari Full support 14WebView Android Full support 85Chrome Android Full support 85Firefox Android Full support 79Opera Android No support NoSafari iOS Full support 14Samsung Internet Android No support Nonodejs No support No

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参见