Pseudo headless arrows

Fabrício Matté ultcombo at
Thu Apr 21 23:09:12 UTC 2016

@John: Good point.
IIRC, Mocha was (is?) one of such test frameworks that inspect the
function's `length` property in order to determine whether the author
intends the test to be run asynchronously (i.e. the first argument receives
a function that must be called when the test is done).
Whether that is a good practice is questionable, however.


On Thu, Apr 21, 2016 at 7:44 PM, John Lenz <concavelenz at> wrote:

> _=>{} is a function that takes one param and is not equivalent to ()=>{}.
> Some test frameworks inspect the function and care about the difference.
> On Apr 21, 2016 3:34 PM, "Fabrício Matté" <ultcombo at> wrote:
> The `==>` token would look like a new operator, which developers would
> have to look up in order to know exactly what it does. It is more confusing
> than helpful, IMHO.
> Also `==>x` has the same length as `_=>x`, the latter not introducing any
> new syntax (although it does employ an ugly unused identifier).
> By the way, this may be of interest to you: Headless Arrow Functions
> proposal <>.
> /fm
> On Thu, Apr 21, 2016 at 3:48 PM, Peter van der Zee <ecma at> wrote:
>> <searched for it><excuses if>
>> There are two ways of writing argument-less arrows;
>> () => x;
>> _ => x;
>> (Where `_` can be any identifier, of course.) I understand why we
>> can't drop the head entirely so if we're forced to type anything at
>> all, anyways, why not at least make it simpler by pressing two
>> different keys instead of three/four:
>> ==> x;
>> I don't believe this leads to syntactical problems anywhere, not even
>> with arrow functions themselves and it's future proof for at least the
>> cases I'm aware of.
>> It's a minor addition but I think it's much nicer than either of the
>> two alternatives we currently have, which lead to a lot of
>> inconsistencies (it's spaces and tabs all over again).
>> Semantics are the same otherwise as `() => x` would be.
>> - peter
>> _______________________________________________
>> es-discuss mailing list
>> es-discuss at
> _______________________________________________
> es-discuss mailing list
> es-discuss at
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the es-discuss mailing list