1.1.3: existential @var? doesn't check for undefined

[lookfirst]

This seems like a pretty minimal test case:

@a?

outputs:

this.a != null;

According to the documentation, "CoffeeScript's existential operator ? returns true unless a variable is null or undefined"

a?

correctly outputs:

typeof a !== "undefined" && a !== null;

[lookfirst]

Most minimal test case does work:

@?

[michaelficarra]

See #1631

[michaelficarra]

Whoops, didn't realise it was you. Here's a more complete explanation: X == null tests that X is either null or undefined, assuming it is in scope. If we can't make that assumption, we need to do a typeof test to avoid ReferenceErrors. Please search for old issues before posting. There has to be a dozen that are exact duplicates.

[lookfirst]

Apologies, I did search, but nothing came up that seemed relevant. There are so many closed issues now that searching through them is tiresome. Thanks for your patience.

It is disappointing that there doesn't seem to be a good solution for this issue. I was hoping to write some code that checked for null or undefined and there doesn't seem to be a good syntactic way to do that in CS.

[michaelficarra]

@lookfirst: X? does check for null or undefined.

$ node
> a = null
null
> a == null
true
> a = void 0
> a == null
true
> a = 0
0
> a == null
false
> 

[lookfirst]

What I'd like to do is write this:

    methodFoo:
        @saveGroup(@d.groupName.val().trim(), @key?)

    saveGroup: (groupName = '', existing = false) =>
        if existing

What I ended up having to write is this:

    methodFoo:
        keyExists = typeof @key != "undefined" && @key != null
        @saveGroup(@d.groupName.val().trim(), keyExists)

    saveGroup: (groupName = '', existing = false) =>
        if existing

Maybe I'm just not understanding things correctly.

[michaelficarra]

@lookfirst: you're not understanding things correctly. @key? is fine, trust me. It produces true if the value of this.key is either undefined or null. Either one. Otherwise, it produces false. The equivalent javascript test that is being performed is this.key == null. Read up on the abstract equality comparison algorithm (section 11.9.3). Pay careful attention to steps 2 and 3.

[alpha123]

@lookfirst: Googling for site:github.com inurl:jashkenas/coffee-script/issues existential operator seems to find a lot of stuff.

[lookfirst]

Ok, thanks for the pointers. I'm understanding things a lot more clearly now. Again, thanks for your patience.

[michaelficarra]

@alpha123: wow, I'm surprised how effective that is. Google's amazing. Thanks for the tip.

[jashkenas]

We should start a drinking game for every time this comes up ;)

[lookfirst]

For all the beer I owe MF, we'd have to check him and his cute fuzzy bear into rehab after it.