Thelogical AND assignment (&&=) operator only evaluates the right operand and assigns to the left if the left operand istruthy.

Try it

let a = 1;let b = 0;a &&= 2;console.log(a);// Expected output: 2b &&= 2;console.log(b);// Expected output: 0

Syntax

x &&= y

Description

Logical AND assignmentshort-circuits, meaning thatx &&= y is equivalent tox && (x = y), except that the expressionx is only evaluated once.

No assignment is performed if the left-hand side is not truthy, due to short-circuiting of thelogical AND operator. For example, the following does not throw an error, despitex beingconst:

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

Specifications

Browser compatibility

See also

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