Question

I just test the “typeof” in javascript, and really don’t know why the result is like this.

/****/

var cota,
    plouto;

alert(typeof plouto/cota); //NaN 

/****/

var cota,
    plouto;

alert(typeof (plouto/cota)); //number

/****/

var cota,
    plouto;

var flo = plouto/cota;

alert(typeof flo); //number 

Answer 1

The first one alerts NaN because the typeof plouto is executed first, and the result is divided by cota. The result of that is not a number, hence NaN. You could imagine it like this:

(typeof plouto) / cota

The second one divides plouto by cota, which is not a number (because both variables are undefined), but the type of NaN is actually Number, which can be confusing!

The same goes for the third example.