Output?

Question

var x=NaN;
var y=" ";
var z=x+y;
alert(z+4); //alerts NaN 4
alert(NaN+4); //alerts NaN

Why is the 2nd alert showing only NaN while the 1st one shows NaN 4 ?

Answer 1

1st one:
NaN + " " + 4 = "NaN " + 4 = "NaN 4"

2nd one:
NaN + 4 = NaN