Dealing with the special NaN value can be tricky in JavaScript. It behaves like a number and not a number at the same time. This lesson explains how to identify it using the isNaN function or the Number.isNaN method.

 

Number.isNaN = Number.isNaN  || function(x) {x !== x}

 

Number.isNaN(NaN) // trueNumber.isNaN("JS") // falseNumber.isNaN("") // false