Nullish coalescing operator (??)

Examples

let userName = null

// If userName is null or undefined, use 'Guest' as the default value.
// Otherwise, use the value of userName.
let displayName = userName ?? 'Guest'

console.log(displayName) // Outputs 'Guest'

let count = 0

// If count is null or undefined, use 1 as the default value.
// Otherwise, use the value of count.
let increment = count ?? 1

console.log(increment) // Outputs 1

let message = ''

// If message is null or undefined, use 'Hello, world!' as the default value.
// Otherwise, use the value of message.
let greeting = message ?? 'Hello, world!'

console.log(greeting) // Outputs 'Hello, world!'

Syntax

The syntax for the nullish coalescing operator is as follows:

expression1 ?? expression2

The left-hand operand (expression1) is evaluated first. If it is null or undefined, the right-hand operand (expression2) is returned. Otherwise, the left-hand operand is returned.

Description

The nullish coalescing operator is a logical operator that is used to provide a default value for a variable that may be null or undefined.

It is similar to the logical OR operator (||), but the nullish coalescing operator only returns the right-hand operand if the left-hand operand is null or undefined, whereas the logical OR operator returns the right-hand operand if the left-hand operand is any falsy value (i.e., a value that is considered false when evaluated in a boolean context).

Specifications

The nullish coalescing operator is specified in the ECMAScript 2020 (ES2020) language specification.

Browser Compatibility

  • Google Chrome (version 80 and later)
  • Microsoft Edge (version 84 and later)
  • Mozilla Firefox (version 74 and later)
  • Safari (version 14 and later)

Similar Operators

There are several other operators in JavaScript that are similar to the nullish coalescing operator, including:

  • The logical OR operator (||): This operator returns the right-hand operand if the left-hand operand is any falsy value (i.e., a value that is considered false when evaluated in a boolean context).
  • The ternary operator (?:): This operator is a conditional operator that allows you to specify a default value for a variable based on a condition. It has the following syntax: expression1 ? expression2 : expression3. If expression1 is truthy, the operator returns expression2. If expression1 is falsy, the operator returns expression3.