As far as I understand, every string is an object in Javascript. Still, it "does not work" as I expect it to be: var a="abc"; //here we get a new string object a.b = 123; //I seem to declare a property "b" of that object alert(a.b); //alerts "undefined" However, if I try to define a string in the "wrong way", everything works as expected var a=new String("abc"); // a.b = 123; alert(a.b); //alerts "123" Why is that so?