Function prompt should return undefined when cancel is pressed

[martin-henz]

Currently, the return value is null. The null value is not part of Source, so this leaves a weird hole in the specs. I propose to return undefined, so that student can write:
const answer = prompt("What is your answer?");
if (answer === undefined) { .... } else { ... }

[martin-henz]

Let's follow whatever JS does.

[jiachen247]

Can we close this issue in light of null being included in the new spec?

default js prompt behavior in the browser also returns null when we cancel the prompt. Shall we keep to this standard?

Students will be allowed to write this instead.

const answer = prompt("What is your answer?"); 
if (answer === null) { .... } else { ... }

[openorclose]

No, I don't think so. We should make sure that null is only used for the empty list and nothing else.

Otherwise, it would create unnecessary confusion over undefined and null.

[jiachen247]

@openorclose that makes sense!

okay, I guess it comes down to if we want to be with the browser implementation based of the html spec for the window object or we want to be consistent with source and maintain null only to terminate the empty list.

Perhaps updating the source documentation to include this would be helpful!

If everyone is agreeable, I think we can close this and move this discussion to the cadet-frontend.

[thomastanck]

Hm, on the contrary I think there is value in following the browser's behaviour. It even says in MDN that it returns null https://developer.mozilla.org/en-US/docs/Web/API/Window/prompt

If we follow the browser behaviour then porting scripts from Source to JS would have a better chance of working.

[openorclose]

Why not we return null, but provide an is_cancel_pressed function to abstract it away?

[thomastanck]

Good idea. I agree.

[martin-henz]

OK, let's do this:
prompt(s)
is_prompt_cancel_pressed(x)

[martin-henz]

I prefer if the function name has "prompt" in it, to make its purpose clear. Would that be ok?