arrow function syntax simplified

Dmitry Soshnikov dmitry.soshnikov at gmail.com
Thu Mar 29 14:57:47 PDT 2012


On Thu, Mar 29, 2012 at 12:02 PM, Brendan Eich <brendan at mozilla.org> wrote:

> Brendan Eich wrote:
>
>> Irakli Gozalishvili wrote:
>>
>>> Few questions on this new arrow functions:
>>>
>>> let foo = x => x * x
>>>
>>>
>>> 1. What is foo.prototype ?
>>> 2. What does new foo(y) does ?
>>>
>>
>> The idea with arrow function syntax (as opposed to block-lambda revival)
>> was to be as close to "just syntax" for functions. Obviously we've made
>> early-error restrictions but this design goal still stands. So the answers
>> are:
>>
>> 1. Same as for any user-defined function (a fresh Object instance).
>> 2. Same as for any user-defined function.
>>
>
> Oops, I left off something important. Since we agreed on lexical |this|
> binding, there's no way for the new object to flow into the arrow function.


Just a small note related to lexical `this' -- if it's just a syntactic
sugar for the `bind' method, then [[Construct]] probably should (for
consistency?) work, providing newly created object -- because a bound
function delegates to the target's [[Construct]] per ES5.

Dmitry



> So I'm wrong, the answers are:
>
> 1. Same as for any built-in function: no .prototype property at all.
> 2. Arrow-functions lack [[Construct]] so you cannot 'new' them.
>
> This makes arrows like built-ins. They're still functions, per my other
> answers.
>
> I'll update the strawman (which should be promoted shortly).
>
> Thanks for the good questions!
>
> /be
>
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