JavaScript Nullish Coalescing Guide

The nullish coalescing operator (??) provides a better way to handle default values when dealing with null or undefined.

Nullish Coalescing Assignment#

Loading code block...

Best Practices#

When to Use ??:
✓ Default values for optional config
✓ API response fallbacks
✓ User input defaults
✓ When 0, '', or false are valid

When to Use ||:
✓ When any falsy value means "use default"
✓ Boolean coercion is desired
✓ Legacy code compatibility

With Optional Chaining:
✓ Use both together: obj?.prop ?? default
✓ Chain from access to default naturally
✓ Handles deep nesting elegantly

Avoid:
✗ Mixing ?? with && or || without ()
✗ Using || when ?? is needed
✗ Forgetting null vs undefined semantics

The nullish coalescing operator (??) provides precise control over default values by only triggering for null and undefined, unlike || which triggers for any falsy value. Use it when zero, empty strings, or false are valid values. Combine it with optional chaining (?.) for elegant handling of potentially missing nested properties. The ??= assignment operator adds convenient lazy initialization patterns.

JavaScript Nullish Coalescing Guide

Basic Syntax#

Why Use Nullish Coalescing#

With Optional Chaining#

Function Parameters#

Object Defaults#

Nullish Coalescing Assignment#

Chaining#

With Logical Operators#

Type Coercion#

Common Use Cases#

TypeScript Integration#

Comparison Summary#

Best Practices#

Conclusion#

Share this article

Related articles

JavaScript Optional Chaining Guide

JavaScript Nullish Assignment Operators Guide

JavaScript BigInt Guide