What is null ? doing in this line of JavaScript

Question

I have this line of code in JS for handing payments, but I'm not sure what it's doing as I've never seen some of this syntactic sugar before.

var fund = response.card != null ? response.card[0] : response.bank_acct[0];

It's the same "syntactic sugar" as in C, PHP, Perl, and a number of other languages. — Barmar, Jan 22 '15 at 17:28
@Barmar: Indeed, or any other language [syntactically derived from B](http://cm.bell-labs.com/who/dmr/kbman.html). :-) (Warning: Link is PDF to B manual.) — T.J. Crowder, Jan 22 '15 at 17:29
It does what the basic language syntax definition says it does. Look up the `?` operator. Also, please give your question a meaningful title, such as "What does the ? operator do in JavaScript?". — , Jan 22 '15 at 17:32
@1nflktd: Yup. I'm not sure BCPL (B's ancestor) didn't have it, but I'm not sure it *did*, either. :-) — T.J. Crowder, Jan 22 '15 at 17:50

score 5 · Accepted Answer · answered Jan 22 '15 at 17:26

5

This is the conditional operator. Instead of writing this:

var fund;
if(response.card != null )
{
    fund = response.card[0]
}
else
{
    fund = response.bank_acct[0];
}

you could write this:

var fund = response.card != null ? response.card[0] : response.bank_acct[0];

answered Jan 22 '15 at 17:26

Christos

@Downvoter could you please explain me where the answer is wrong? Thank you in advance. – Christos Jan 22 '15 at 17:40
Nothing wrong with your answer per se, but I question encouraging the use of SO as a Q&A resource for people who have not bothered to learn the basic syntax of the language. You also could have pointed him to authoritative pages about `?`, and/or given suggestions to him about how to find such resources on his own, so he doesn't have to post to SO every time he sees a syntactic construct he doesn't know, and/or commented on its long history in other programming languages, and/or commented on why one form might be preferred to the other in what kinds of cases. – Jan 22 '15 at 17:58

Andy · Answer 2 · 2015-01-22T18:02:50.793

3

It works the same as (and is considered shorthand for) this conditional statement:

var fund;
if (response.card != null) {
  fund = response.card[0];
} else {
  fund = response.bank_acct[0];
}

edited Jan 22 '15 at 18:02

answered Jan 22 '15 at 17:28

Andy

1

your triple equals should be assignments, shouldn't they? – Mic Jan 22 '15 at 17:30
1

End of a long day. Thanks for the catch. – Andy Jan 22 '15 at 17:30

2 Answers2