In CoffeeScript, what is the existential operator for and how do you use it?

Question

I see all sorts of questions about the existential operator on SO, but none of them ask the fundamental question of "what is it for" and "how do you use it?" so I thought I'd ask this here.

The answer here would probably suffice as an answer to this question, but the problem is the question title doesn't suggest that. As a result, it's very hard to find this question by a google search. So, my intention here is to make it easier to learn what this operator does from a google search.

BTW, I am aware of the section in the The Little Book on CoffeeScript titled "Aliases & the Existential Operator", but for some reason I don't like its explanation. It doesn't make me feel like "I get it".

Why didn't you just change the title of the original question, as others have suggested? — Robert Harvey, Aug 07 '13 at 17:31
@RobertHarvey I didn't know I could do that since I didn't write it. I'll do that in the future. — Daniel Kaplan, Aug 07 '13 at 17:50

Peter Lyons · Accepted Answer · 2013-08-07T17:58:51.127

1

The existential operator provides a more concise and expressive way to handle null and undefined properties.

Instead of

if (user && user.url && user.url.indexOf('foo'))

you can do

if user?.url?.indexOf 'foo'

Instead of

if (baker.bakeBread) { baker.bakeBread()}

you can do coffeescript

baker.bakeBread?()

edited Aug 07 '13 at 17:58

answered Aug 07 '13 at 17:35

Peter Lyons

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OK great answer. Even more concise and helpful than what I linked to. – Daniel Kaplan Aug 07 '13 at 17:53

In CoffeeScript, what is the existential operator for and how do you use it?

1 Answers1