JavaScript - Why can't I add new attributes to a “string” object?

Question

I\'ve experimented with JavaScript and noticed this strange thing:

var s = \"hello world!\";
s.x = 5;
console.log(s.x); //undefined

Every t

Answer 1

A string in JavaScript isn't an instance of String. If you do new String('my string') then it will be. Otherwise it's a primitive, which is converted to a String object on the fly when you call methods on it. If you want to get the value of the string, you need to call toString(), as shown below:

var s = new String("hello world!");
s.x = 5;
console.log(s.x); //5
console.log(s); //[object Object]
console.log(s.toString()); //hello world!