Hi Ben, Thanks for the help. I wanted to give it a week to soak in before I replied again :)
The final piece clicked into place when I realized (for the second time, since I definitely learned this then forgot, heh) was that FunctionTemplate is per-isolate, but a Function is per-context. Whatever I add to a FunctionTemplate will exist in all contexts (because FunctionTemplate is per-isolate), while whatever I add to a Function returned from FunctionTemplate::GetFunction will only exist in the context I specified in the call to GetFunction (or whichever context is the current one in the isolate). On Friday, January 15, 2021 at 3:23:04 AM UTC-8, Ben Noordhuis wrote: > > On Fri, Jan 15, 2021 at 1:48 AM Ron Prestenback > <ronpres...@gmail.com <javascript:>> wrote: > > > > Hi Ben, thanks for the reply! I have worked with C++ for many years but > this is my first exposure to javascript. I'm using the web editor for > replying to this, so apologies if the formatting gets messed up :) I'll > try to do inline quotes as well but not sure how that will turn out, so > I'll try to space them out to help readability. > > > > I have read over the doc on prototypal inheritance here: > https://javascript.info/prototype-inheritance and > https://javascript.info/function-prototype I assume that covers all the > important stuff? > > > >> - Constructors return an object > >> - The prototype template is used to configure that object's prototype > > > > > > Why wouldn't the object's prototype be the instance template? The > object returned by the constructor is an instance, right? And the object's > prototype would the "template" the instance was configured from, no? I'm > starting to suspect that "prototype" and "template" have completely > different meanings in v8, whereas in standard usage these terms are > synonyms. This is where I get confused, I guess.... > > "Prototype" has a very specific meaning in JS - it's the chain of > objects that are searched to resolve properties that don't exist in > the instance. > > Example: var x = o.x; > > If o looks like { x: 42 }, then o.x is an instance property, but > otherwise the prototype of o is searched, then the prototoype of the > prototype, and so on. To illustrate: > > var A = { x: 42 }; > var B = { __proto__: A }; > var o = { __proto__: B, y: 1337 }; > var x = o.x; // Searches the chain until it finds A.x > var y = o.y; // But this lives in the instance > > "Template" is just V8 parlance. The template describes the "shape" of > the prototype or instance object. > > One way to think about templates is that they're an optimization that > lets V8 allocate the needed space for an object (or prototype) > upfront. > > > > >> > What is the difference between a prototype template and an instance > template? > >> It's the difference between `this` and `this.__proto__`, or: > >> function F() { > >> this.x = 42; > >> } > >> F.prototype.y = 1337; > > > > > > Sorry I'm really trying but I'm not sure how to apply your answer to my > question. In your example, F.prototype would be the same as the __proto__ > object for all instances of 'F', right? > > Correct. > > > If I'm understanding correctly (which is doubtful), in v8 parlance that > makes F.prototype the instance template of F, right? If not, which thing is > the instance template? > > The body of F (the line that sets `this.x = 42`) corresponds with the > instance template. > > >> > If I have a constructor function that I want to run when the new > objects of the class are created, where should that go? > >> FunctionTemplate. Methods are set with > FunctionTemplate::PrototypeTemplate(). > >> (Technically you can also set them on the instance template but that's > >> kind of pointless.) > > > > > > Oh, why would it be pointless to set a method on an InstanceTemplate? > > Because you use the InstanceTemplate for values that are likely > different between different instances of the same class (think: a > Point class with x and y coordinates). > > Methods on the other hand don't normally change so those belong on the > prototype. > > >> > Depending on the answers to the previous 3, this question may be > moot, but: Is there any reason to have the same function or property on two > or more of these "entities"? FunctionTemplate and Function? Or Function > and PrototypeTemplate? etc. For example, I have some existing code that is > first setting a property (via Set) on the PrototypeTemplate of the > FunctionTemplate, then it also sets that same property (with same value) on > the FunctionTemplate. What might be the intent here? > >> Probably to make it available as both a method and a class method: > >> o.m() and F.m() > > > > > > OK, that makes sense. What would the difference be if I set that > property on the InstanceTemplate instead? Or to put another way, why would > I ever set something on an InstanceTemplate instead of a PrototypeTemplate? > > See above. :-) > -- -- v8-users mailing list v8-users@googlegroups.com http://groups.google.com/group/v8-users --- You received this message because you are subscribed to the Google Groups "v8-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to v8-users+unsubscr...@googlegroups.com. 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