//typeof() will return the type of value in it's parameters.
//some examples of types: undefined, NaN, number, string, object, array
//example of a practical usage
if (typeof(value) !== "undefined") {//asuming value is already set
//execute code
}
// You can use the built-in method 'typeof' in order to check the variable datatype
//examples:
typeof "hello" // "string"
//or
var a = 1;
typeof(a);
//the output will be > 'number'