Array.prototype.filter doesn't require callback to return

I dig a bit and found out in #5850 and subsequently in #7779 the signature of filter has been changed not to return a boolean, so that people could return a truthy value in the implementation of the filter.

While I undertand the convenience in terms of ease of use, this as far as I observed puts developers at risk of simple bugs like the following:

const even = [1,2,3].filter(x => {
    x % 2 == 0
})

Notice the missing return statement means the function returns undefined, which translates to false, which filters all the items out. This applies also in the case of noImplicitReturns set to true, since the function return type is any, thus it could be a void function for what the compiler knows.

I believe TypeScript's job should be to put this kind of cases in check actually, so that things like truthy values (which sometimes aren't as obvious as we might think and introduce bugs we don't really understand) can be better taken care of.

One solution to make both parties happy would be to optionally support truthy values (maybe an extra compiler flag? Another truthy type to allow for more relaxed checking?) and reintroduce the original signature of filter.

Commencez par examiner la signature de Array.prototype.filter et l’historique des issues #5850 et #7779. Déterminez si la vérification demandée doit rejeter les callbacks qui omettent les instructions return tout en préservant le comportement prévu pour les valeurs truthy ; l’issue est terminée lorsque le comportement souhaité de la vérification de types et les compromis de compatibilité sont spécifiés et couverts par des tests de compilateur appropriés.