A comment by Vítor De Araújo on a blog post by Douglas Crockford points out that the two are not the same. He gives an example showing that a string is not like an object:
A string object and a string value are not the same thing:
js> p = "Foo" Foo js> p.weight = 42 42 js> p.weight // Returns undefined js> q = new String("Foo") Foo js> q.weight = 42 42 js> q.weight 42The string value cannot have new properties. The same thing is valid for other types.
What is going on here that an string is not an object? Am I confusing JavaScript with some other languages, where everything is an object?
"Everything is an object"... that's one of the big misconceptions that exist all around the language.
Not everything is an object, there are what we call primitive values, which are string, number, boolean, null, and undefined.
That's true, a string is a primitive value, but you can access all the methods inherited from String.prototype as if it were an object.
The property accessor operators (the dot and the bracket notation), temporarily convert the string value to a String object, for being able to access those methods, e.g.:
"ab".charAt(1); // "b"
What happens behind the scenes is something like this:
new String("ab").charAt(1); // "b", temporal conversion ToObject
As with the other primitive values, such as Boolean, and Number, there are object wrappers, which are simply objects that contain the primitive value, as in your example:
var strObj = new String("");
strObj.prop = "foo";
typeof strObj; // "object"
typeof strObj.prop; // "string"
While with a primitive:
var strValue = "";
strValue.prop = "foo";
typeof strValue; // "string"
typeof strValue.prop; // "undefined"
And this happens because again, the property accessor on the second line above, creates a new temporal object, as:
var strValue = "";
new String(strValue).prop = "foo"; // a new object which is discarded
//...