Impossible JavaScript Question

test.js

/* what do each of these statements return?
   (assume that they are evaluated individually but in order.)
*/

const foo = 'asdf'; //=> ?

foo.bar = 12345; //=> ?

foo; //=> ?

foo.bar; //=> ?

Object.getOwnPropertyNames(foo); //=> ?

What is the point? Are you trying to show that people don't know what assignment statements are going to return? I think that's true in most languages because it's so unusual to use the return value of an assignment for anything.

I think there's value in showing that a language does weird things when used in common ways, but if you do something unusual (like adding new properties to a string), of course most people won't know what will happen.

(I'm not a fan of JS at all, just not sure this is the way to convince people that it's a bad tool.)

Hehe. This is actually derivative of some code I found that took me and another programmer some time to split up and figure out what it was doing and if that's even possible. What really got me is that the assigning to a property of a string seems like it should throw an error but it doesn't (in most JS environments). So we turned it into a reduced test case and started asking people to solve it. It's not really for proving that people don't know JS or making a huge statement about the language. It's an illustration of what happens when you write really weird/bad code. As an extra bit of fun, it's a nifty way to pry at how people thing the language does and should work.

I didn't realise the second one behaved differently without strict mode. Are we assuming non-strict?

What's the use of knowing this? You wouldn't do it in production so who cares?

@EionRobb - I hadn't even thought about strict mode yet. Good catch!
@mgd020 - Shits and giggles lol. This actually came up because of production code so somebody did it in production.
@gkaykck - Haha. Well done ;). I absolutely don't expect people to know this stuff by heart. That's why it's such a weird challenge. This isn't stuff that you should know because you should never be doing this nonsense to begin with.