Logical Assignment Operators

Logical Assignment Operators was introduced in the ECMAScript 2021 update. It is a new feature that combines the assignment operators with the logical operators (||, &&, ??). It that allows you to assign a value to a variable if true (&&=), false (||=) or null (??=).

Types of Logical Assignment Operators

• Logical OR assignment operator ||=
• Logical AND assignment operator &&=
• Nullish coalescing assignment operator ??=

Logical OR assignment operator ||=

This accessor is used to assign a value to a variable if the variable is not already assigned. If the variable is already assigned, the value is not changed.

//Syntax

a ||= b

This syntax is also similar to:

if (!a) {
  a = b
}

An example is

let a = 0
a ||= 1
console.log(a) // 1

The above example assigns the value 1 to the variable a if the variable is not already assigned. If the variable is already assigned, the value is not changed.

Logical AND assignment operator &&=

This is used to assign a value to a variable only if the value is a truthy

// Syntax

a &&= b

This syntax is also similar to:

if (a) {
  a = b
}

An example is

let a = 0
a &&= 1
console.log(a) // 0

In the above example, a is a falsy value, so it will not be reassigned. It will only reassign if the value is truthy.

let a = 4
a &&= 1
console.log(a) // 1

Nullish coalescing assignment operator ??=

This is similar to the Logical OR assignment operator ||=, however, it only reassigns if the left operand is null or undefined.

// Syntax

a ??= b

This syntax is also similar to:

if (typeof a === "undefined" || a === null) {
  a = b
}
let a = 0
a ??= 1
console.log(a) // 0
let b = null
b ??= 1
console.log(b) // 1