null and undefined

The two empty values are loosely equal but strictly different.

In 2026: Still works. null == undefined is true by a special rule in the == algorithm; the two are the language's two ways of saying nothing. But they are different types, so null === undefined is false, and typeof null is "object" while typeof undefined is "undefined".

Where it came from: The == algorithm has a clause making null and undefined equal to each other and nothing else, as MDN's null page notes. MDN ↗

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