Logical AND assignment (&&=)
The logical AND assignment (&&=
) operator only evaluates the right operand and assigns to the left if the left operand is {{Glossary("truthy")}}.
{{EmbedInteractiveExample("pages/js/expressions-logical-and-assignment.html")}}
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 (
&=
) - {{Glossary("Truthy")}}
- {{Glossary("Falsy")}}