Introduction to DataTypes and Values

Empty values

There are two special values, written null and undefined, that are used to denote the absence of a meaningful value. They are themselves values, but they carry no information.

Many operations in the language that don't produce a meaningful value (you'll see some later) yield undefined simply because they have to yield some value.

The difference in meaning between undefined and null is an accident of JavaScript's design, and it doesn't matter most of the time. In cases where you actually have to concern yourself with these values, I recommend treating them as mostly interchangeable.