JavaScript Nullish Coalescing(??) Operator

Last Updated : 15 Jan, 2026

The nullish coalescing (??) operator is used to handle null and undefined values in JavaScript. It allows you to assign a default value when a variable does not have a valid value.

  • It returns the right-hand value only when the left-hand value is null or undefined.
  • It does not treat 0, false, or empty strings as nullish values.
  • It is useful for setting safe default values without overwriting valid data.

Example 1: In this example, we will see a basic function using the nullish coalescing operator

javascript 
function foo(bar) { 
    bar = bar ?? 55; 
    console.log(bar); 
} 
foo(); // 55 
foo(22); // 22

Syntax:

variable ?? default_value

Example 2: The more common use case is to set default values for JSON objects as follows. 

javascript 
const foo = { 
    bar: 0 
} 

const valueBar = foo.bar ?? 42; 
const valueBaz = foo.baz ?? 42; 

// Value of bar: 0 
console.log("Value of bar: ", valueBar); 

// Value of bar: 42 
console.log("Value of baz: ", valueBaz);

Best Practices

  • Use ?? when you only want to handle null or undefined.
  • Avoid mixing ?? with || in the same expression without parentheses.
  • Prefer ?? for default values in configuration and API responses.

Supported Browsers: The browsers supported by JavaScript Nullish Coalescing Operator are listed below:

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Article Tags:
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javascript-operators

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