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  • Comments on “Making Built-in Objects Subclassable”

Comments on “Making Built-in Objects Subclassable”

# Axel Rauschmayer (13 years ago)

A few more thoughts:

  • This marks the end of prototypal inheritance in JavaScript (not complaining, just stating a fact). Putting @@create in constructors C makes a lot of sense, but it could, in principle, also be put into instance prototypes C.prototype. Then Object.create(proto) could use @@create to create the instance whose prototype is proto.

  • I would love to have a @@postConstruct method (similar to @@create) that is invoked after all constructors are done with initialization. Use case: freeze an instance or make it non-extensible.

  • Slide 24: marking objects as initialized in the root of a class hierarchy looks suspicious to me (the constructors are not done initializing, yet!). Doing it in something like @@postCreate might make more sense.

Axel

# Herby Vojčík (13 years ago)

Axel Rauschmayer wrote:

A few more thoughts:

  • This marks the end of prototypal inheritance in JavaScript (not complaining, just stating a fact). Putting @@create in constructors C makes a lot of sense, but it could, in principle, also be put into instance prototypes C.prototype. Then Object.create(proto) could use @@create to create the instance whose prototype is proto.

The identifier create is probably used in lots of other places, so this is non-starter, but if not, it could be simply reused, so that:

Ctr.create(proto, [descriptors])

does

newobj = Ctr@@create; newobj.proto = proto; Object.defineProperties(newobj, descriptors);

It is semantically compatible with what Object.create does now. In fact, if somewhere inside implementation of Object.create one would use "this[@@create]" to create new instance, and it was moved to Function.prototype, it could be used as is.

# Herby Vojčík (13 years ago)

Herby Vojčík wrote:

Axel Rauschmayer wrote:

A few more thoughts:

  • This marks the end of prototypal inheritance in JavaScript (not complaining, just stating a fact). Putting @@create in constructors C makes a lot of sense, but it could, in principle, also be put into instance prototypes C.prototype. Then Object.create(proto) could use @@create to create the instance whose prototype is proto.

The identifier create is probably used in lots of other places, so this is non-starter, but if not, it could be simply reused, so that:

Ctr.create(proto, [descriptors])

does

newobj = Ctr@@create; newobj.proto = proto; Object.defineProperties(newobj, descriptors);

Sorry for replying to myself, but another possibility is to add proto and descriptors parameters to IIRC parameterless @@create. Object.create would thus just point to Object[@@create] and others could be create similarly: Array[@@create](myprototype, mydescriptors);