err,
try {
let thisValue = this; //can't reference 'this' prior to
'super()' in a [[Construct]] call of a derived function
} catch (e} {
calledAsFunction = false //no let here
}
On Jan 16, 2015, at 12:02 PM, Allen Wirfs-Brock wrote:
>
> On Jan 16, 2015, at 11:40 AM, Kevin Smith wrote:
>
>> Changes include: Updated specification to use and support the new built-in
>> subclassing scheme described at:
>> https://github.com/tc39/ecma262/blob/master/workingdocs/ES6-super-construct%3Dproposal.md
>>
>> This looks nice. An interesting question:
>>
>> For classes that have divergent [[Construct]]/[[Call]] behavior, should the
>> [[Call]] behavior be "inherited" by derived classes?
>>
>> class MyDate extends Date {}
>> console.log(MyDate(1, 2, 3)); A string, or throw an error?
>>
>>
>
> Since the above class definition does not include an explicit constructor
> body, it gets the equivalent of
> constructor(...args) {super(...args)}
> as its implicit constructor definition
>
> A 'super()' call throws if the NewTarget is null (ie, if the constructor is
> invoked via [[Call]] )
>
> If you want to inherit call behavior you need to code it as:
>
> class MyDate extends Date {
> constructor(...args) {
> if (new.target===null) return super.constructor(...args)
> super(...args);
> }
> }
>
> That's assuming 'new.target' makes it into ES6. Without it you would have to
> do something like:
>
> class MyDate extends Date {
> constructor(...args) {
> let calledAsFunction=true;
> try {
> let thisValue = this; //can't reference 'this' prior to
> 'super()' in a [[Construct]] call of a derived function
> } catch (e} {
> let calledAsFunction = false
> }
> if (calledAsFunction) return super.constructor(...args)
> super(...args);
> }
> }
>
> Allen
> _______________________________________________
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