Why do Javascript primitive values (e.g. name = “John”) have properties and methods? [duplicate]

Answer 1

They don't. However, whenever you access a property (method) on them they're implicitly casted to a wrapper object.

var name = "John";
name.toLowerCase(); // typeof name == "string"
// what happens is:
(new String(name)).toLowerCase() // typeof new String(name) == "object"

Answer 2

They don't. Primitive values have neither properties nor methods.

But when you do

var s = " a ";
var b = s.trim();

the value of s is promoted to a String object (not a primitive string) just for this operation.

It's the same for numbers and booleans.

You can check you don't really attach properties to primitive values with this code :

var s = "a";
s.prop = 2;
console.log(s.prop); // logs undefined

It logs undefined because the property was attached to a temporary object, an instance of String, not to s. If you wanted to keep the property, you'd have done

var s = new String("a");
s.prop = 2;
console.log(s.prop); // logs 2