Adding properties to variables in javascript

Question

Consider the following codes:

var str = "abc";
 str.foo = 123;  // write - ignored
123
 str.foo  // read
undefined

Why do I get undefined? Shouldn't that property output 123? What is the reason for it outputting undefined?

Since var str is a string, why don't properties show up a second time?

Cant we add properties and methods to a string?

score 0 · Answer 1 · edited May 23 '17 at 10:32

0

You are defining str as a string, not an object. Maybe you meant to do something like this:

var o = {};
o.str = "abc";
o.foo = 123;

See the selected answer to this question for lots of great detail:

edited May 23 '17 at 10:32

Community

answered Apr 02 '13 at 15:41

lbstr

2

str = new String("abc"); – dyurkavets Apr 02 '13 at 15:43
This question is on the way to being closed as a duplicate. see here http://meta.stackexchange.com/questions/82420/remove-rep-gained-from-answering-a-question-that-is-a-duplicate for why you shouldn't answer these types of questions. – Ryan Apr 02 '13 at 15:52
@frontendmagic I just deleted a comment questioning why you wrote that, but after a quick test, its quite clear. `typeof new String("abc")` is `object` whereas `typeof "abc"` is `string`. Thanks for the comment! – lbstr Apr 02 '13 at 16:05

1 Answers1