JavaScript defines two special types, which both have only one value assigned: null and undefined.

Those are very special.


null is a special value that indicates the absence of a value.

It’s a common concept in other languages as well, can be known as nil or None in Python for example.


undefined indicates that a variable has not been initialized and the value is absent.

It’s commonly returned by functions with no return value. When a function accepts a parameter but that’s not set by the caller, it’s undefined.

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