The &&= operator only evaluates the right operand and assigns to the left if the left operand is truthy.

Try it

let a = 1;
let b = 0;

a &&= 2;
console.log(a);
// Expected output: 2

b &&= 2;
console.log(b);
// Expected output: 0

Syntax

x &&= y

Description

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

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;

Neither would the following trigger the setter:

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

x.value &&= 2;

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

Specifications

Browser compatibility

See also

• Logical AND (&&)
• Nullish coalescing operator (??)
• Bitwise AND assignment (&=)
• Truthy
• Falsy