The logical AND assignment (&&=) operator only evaluates the right operand and assigns to the left if the left operand is
.
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