Null and Undefined

JavaScript has two special values for "nothing": null and undefined. They're similar but have important differences.

undefined

A variable is undefined when declared but not assigned a value:

null

null is an intentional absence of value - you assign it explicitly:

Checking for null/undefined

Nullish Coalescing (??)

The ?? operator returns the right side if the left is null or undefined:

Exercise: Default Values

Use nullish coalescing to provide a default value:

Exercise: Check Undefined

Check if a variable is undefined: