But what the heck is it? It’s not really that complicated. Think of
undefined as the value assigned to things that don’t yet have a value (in other words they haven’t been initialized).
So what good is it? Well,
undefined gives you a way to test to see if a variable (or property, or array item) has been given a value. Let’s look at a couple of examples, starting with an unassigned variable:
- 7. Types, Equality, Conversion and All That Jazz: Serious types
- Publisher: O'Reilly Media, Inc.
- Released: March 2014
What is Undefined? A tip: undefined is anything that either has not been (initialized/declared/defined) or (anything that has not been given a value)