IsConstructor

[André Bargull]

On 6/11/2014 5:40 PM, Alexandre Morgaut wrote:
>
> On 11 juin 2014, at 17:11, André Bargull <andre.bargull at udo.edu> wrote:
>
>>> Quick note: that isConstructor isn't really viable unless you plan on using
>>> it with constructors that do not have side effects.
>>>
>>> Rick
>>
>> The Proxy-based solution needs to be used in these cases. Now we just need to wait until Proxies are available everywhere! ;-)
>>
>
>
> Not sure Proxy solve anything when we want to test the constructor nature of a function and be sure invoking it won't change anything in the current application context
>
> To highlight what side-effects mentioned by Rick could be, a tested function while invoked may:
> - do DOM Manipulations,
> - change properties in the global object,
> - initiate Web Sockets or Web Workers...
>
> Not safe at all...
>

 From [1]:
```javascript
function IsConstructor(o) {
   try {
     new (new Proxy(o, {construct: () => ({})}));
     return true;
   } catch(e) {
     return false;
   }
}
```

This IsConstructor implementation does not trigger any side-effects and 
works even when the underlying constructor requires arguments etc.



[1]
https://github.com/anba/es6draft/blob/master/src/test/scripts/suite/lib/assert.js#L53-L60


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> Alexandre Morgaut
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