NaN !== NaN

So there I was, minding my own business, again writing JavaScript tests… when suddenly I wanted to write a test to see what happens if NaN was supplied as a parameter.

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NaN

Stands for “Not A Number”.  You can get a NaN in a few different ways:

But when checking for NaN, there’s only one way:

isNaN()

isNaN takes the variable and returns a boolean – true if the value is NaN, otherwise false.  If you try to check for NaN in any other way:

…It doesn’t work.  So make sure you just use isNaN(), ok?

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