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

Primitives MDC docs are immutable.

primitive, primitive value
A data that is not an object and does not have any methods.
JavaScript has 5 primitive datatypes: string, number, boolean, null, undefined.
With the exception of null and undefined, all primitives values have object equivalents which wrap around the primitive values, e.g. a String object wraps around a string primitive.
All primitives are immutable.