Factory class

[tc39]

Factory class

[bakkot]

Among other things, factory functions cannot readily create instances which can interact with each other's private fields, not build brand checking methods like Array.isArray.

[kofifus]

Hey bakkot, thanks for replying.

factory functions cannot readily create instances which can interact with each other's private fields

I am confused as to why this is a desirable thing.. Can you please refer me to the part of the suggested standard that talks about this ? is this something like C++ friend mechanism ?

not build brand checking methods like Array.isArray

Isn't that what instanceOf is for ? (which can easily be supported as is in the above mentioned solution)

[bakkot]

No, not like friend. See the faq. This is how it works in almost all languages with some notion of "private fields", and is useful for making methods like "equals".

instanceof is not a reliable brand check, since prototypes can be changed.

[kofifus]

Ah I see,

brand check can pretty easily be added to factory. However such an equals method cannot.

[littledan]

Some more advantages: More straightforward for a JIT to optimize, and more ergonomic.