Nullish coalescing
The nullish coalescing (??) operator is a logical operator that returns its right-hand side operand when its left-hand side operand is null or undefined, and otherwise returns its left-hand side operand.
Browser support
| Feature | Desktop | Mobile | ||||
|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Safari | Chrome Android | Safari iOS | |
| 80 | 80 | 72 | 13.1 | 80 | 13.4 | |
| Other | ||||||
| The nullish coalescing assignment (??=) operator, also known as the logical nullish assignment operator, only evaluates the right operand and assigns to the left if the left operand is nullish (null or undefined). | 85 | 85 | 79 | 14 | 85 | 14 |
Syntax
const value = null ?? 'default'; // 'default'
const zero = 0 ?? 'default'; // 0
const empty = '' ?? 'default'; // ''
// Difference from ||
0 || 'default'; // 'default' (0 is falsy)
0 ?? 'default'; // 0 (0 is not null or undefined)Live demo
Defaults without losing zero
Compare || and ?? to see why numeric zero often needs the nullish version.
Configuration fallback
Apply defaults only to missing options while keeping explicit empty or false values.
Use cases
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Applying defaults safely
Keep explicit values such as 0 or an empty label instead of replacing them accidentally.
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Reading optional settings
Use ?? when configuration objects may omit a field but should preserve intentionally empty values.
Cautions
- ?? is about missing values only; if falsy values should also fall back, || may still be the right tool.
- Mixing ?? with || or && requires parentheses in JavaScript syntax.
Accessibility
- When you preserve empty strings intentionally, make sure the interface still exposes an accessible label or help text elsewhere.