typeof

A less-known operator in JavaScript is the typeof operator. It tells you what type of data you're dealing with. Makes sense, huh? Let's look at some examples:

var BooleanValue = true;
var NumericalValue = 354;
var StringValue = "This is a String";
alert(typeof BooleanValue) // displays "boolean"
alert(typeof NumericalValue) // displays "number"
alert(typeof StringValue) // displays "string"