逻辑与赋值 (&&=)

¥Syntax

x &&= y

¥Description

逻辑 AND 赋值 short-circuits，意味着 x &&= y 等价于 x && (x = y)，只不过表达式 x 仅计算一次。

¥Logical AND assignment short-circuits, meaning that x &&= y is equivalent to x && (x = y), except that the expression x is only evaluated once.

如果左侧由于 逻辑与 运算符短路而不为真，则不会执行任何分配。例如，尽管 x 是 const，但以下内容不会引发错误：

¥No assignment is performed if the left-hand side is not truthy, due to short-circuiting of the logical AND operator. For example, the following does not throw an error, despite x being const:

const x = 0;
x &&= 2;

以下内容也不会触发设置器：

¥Neither would the following trigger the setter:

const x = {
  get value() {
    return 0;
  },
  set value(v) {
    console.log("Setter called");
  },
};

x.value &&= 2;

事实上，如果 x 不为真，则根本不会评估 y。

¥In fact, if x is not truthy, y is not evaluated at all.

const x = 0;
x &&= console.log("y evaluated");
// Logs nothing

¥Examples

¥Using logical AND assignment

let x = 0;
let y = 1;

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

¥See also

• 逻辑与 (&&)
• 空合并运算符 (??)
• 按位与赋值 (&=)
• Truthy
• Falsy