Isiah, here's the [rollup.js result](http://goo.gl/jl1B8H) using my setup functions technique. When I paste the result in my console it complains that A is undefined inside the `setUpA` function, which seems odd. Here's the [result of my original code](http://goo.gl/cbjVOi) (similar to your example), and as you can see it will evaluate B first in which case C will be undefined and throw an error.
Bradley, true, but C is also child of A, so it can also make sense to evaluate C before A. They are children of each other. In that case, what is the correct order of evaluation? */#!/*JoePea On Wed, Aug 10, 2016 at 12:47 PM, Bradley Meck <[email protected]> wrote: > Please note that in https://tc39.github.io/ecma262/#sec-moduleevaluation > , Modules evaluate their children prior to evaluating > themselves (15.2.1.16.5.6.c) , C should never be evaluate before A or B > in this dep graph. > > On Wed, Aug 10, 2016 at 2:41 PM, /#!/JoePea <[email protected]> wrote: > >> Oh! And although I think that my `setUpA` and `setUpB` technique should >> work due to the fact that Webpack and Meteor load the modules in the exact >> same order where the C module is executed last, this may in fact fail in >> some other ES6 environment that happens to execute the C module first, in >> which case `setUpA` and `setUpB` will be undefined when C is evaluated. >> >> So, I don't know if my solution is good. I am wondering if there's >> something in the spec that guarantees that the C module evaluates last? >> >> */#!/*JoePea >> >> On Wed, Aug 10, 2016 at 12:38 PM, /#!/JoePea <[email protected]> wrote: >> >>> Isaiah, also note that >>> >>> ```js >>> export default class Foo {} >>> ``` >>> >>> does not create a live binding that can be modified at a later point in >>> time, which is the feature that my `setUpA` and `setUpB` functions are >>> theoretically relying on (and which I believe the Meteor and Webpack >>> environments don't handle properly if I understand live bindings correctly). >>> >>> */#!/*JoePea >>> >>> On Wed, Aug 10, 2016 at 12:31 PM, /#!/JoePea <[email protected]> wrote: >>> >>>> In your module B, `class B` should `extends C` instead of A, so both >>>> classes `A` and `B` extend from `C`. >>>> >>>> I made a reproduction that you can run (assuming you have Meteor >>>> installed). See the following with instructions: >>>> https://github.com/meteor/meteor/issues/7621#issuecomment-238923360 >>>> >>>> But, anyways, the example you just gave is almost identical to my >>>> [original example](https://esdiscuss.org/topic/how-to-solve-this-basic >>>> -es6-module-circular-dependency-problem#content-0) (except for my `B` >>>> class extends from the `C` class). >>>> >>>> I can make a reproduction of that too if you want, but what happens is >>>> that the environment will try to execute module A before executing module >>>> C, at which point `C` is `undefined` inside of module `A`. Basically, the >>>> result would be the same as writing: >>>> >>>> ```js >>>> class A extends undefined {} // throws an Error >>>> ``` >>>> >>>> I noticed that both Meteor and Webpack will try and execute modules A >>>> and B *first*, then finally C, so I thought I could export the setup >>>> functions andrun them after defining the C class so that even if modules A >>>> and B run first the actual class definitions would run after the C class >>>> definition. You can see that I'm trying to take advantage of "live >>>> bindings" in order for this to work (but it didn't, hence I have to pass C >>>> into the setup functions). >>>> >>>> I have a feeling that both Meteor's and Webpack's implementations >>>> aren't up-to-spec as far as live bindings with circular dependencies, but I >>>> could be wrong. >>>> >>>> > You shouldn't need a `setUpA` export, especially called by one of its >>>> dependencies. Just declare and initialize that crap when it's being >>>> declared. >>>> >>>> That's what I thought at first too, but it's not the case, and I'm >>>> trying to find a solution. >>>> >>>> */#!/*JoePea >>>> >>>> On Wed, Aug 10, 2016 at 2:41 AM, Isiah Meadows <[email protected]> >>>> wrote: >>>> >>>>> First of all, I'll point out that even if it's an internal API, you >>>>> should just initialize them immediately. You already have an otherwise >>>>> fully initialized C, so you should just add them whenever it comes. You >>>>> shouldn't need a `setUpA` export, especially called by one of its >>>>> dependencies. Just declare and initialize that crap when it's being >>>>> declared. >>>>> >>>>> ```js >>>>> /* index.js */ >>>>> import A from './app/A' >>>>> console.log('Entrypoint', A) >>>>> ``` >>>>> >>>>> ```js >>>>> /* app/A.js */ >>>>> import C from './C' >>>>> >>>>> export default class A eclxtends C { >>>>> // ... >>>>> } >>>>> >>>>> // set up A here >>>>> console.log('Module A') >>>>> ``` >>>>> >>>>> ```js >>>>> /* app/B.js */ >>>>> import C from './C' >>>>> >>>>> export default class B extends A { >>>>> // ... >>>>> } >>>>> >>>>> // set up B here >>>>> console.log('Module B') >>>>> ``` >>>>> >>>>> ```js >>>>> /* app/C.js */ >>>>> import A from './A' >>>>> import B from './B' >>>>> >>>>> export default class C { >>>>> constructor() { >>>>> // this may run later, after all three modules are evaluated, >>>>> or >>>>> // possibly never. >>>>> console.log(A) >>>>> console.log(B) >>>>> } >>>>> } >>>>> >>>>> // set up C >>>>> console.log('Module C') >>>>> ``` >>>>> >>>>> What's your full output, anyways? That would help me best explain >>>>> what's going on, though. >>>>> >>>>> On Wed, Aug 10, 2016, 02:47 /#!/JoePea <[email protected]> wrote: >>>>> >>>>>> When I try this same code with Webpack, I get the *exact same >>>>>> results*: the `console.log` statements in the exact same order, where the >>>>>> last output shows that `A` in the entry point is `undefined`). >>>>>> >>>>>> Am I misunderstanding something about live bindings? Is there some >>>>>> guaranteed order in which these modules should be evaluated? >>>>>> >>>>>> The reason why I'm after a solution for the circular dependency is >>>>>> because in my real-world case I need to use `instanceof A` and `intanceof >>>>>> B` within the `C` superclass defined in module C. This is a case of the >>>>>> Fragile Base Class Problem where a class should usually *not* have >>>>>> knowledge of it's subclasses, but the base class in my case is intended >>>>>> to >>>>>> be internal only, not a part of the public API that end users will extend >>>>>> from. >>>>>> >>>>>> */#!/*JoePea >>>>>> >>>>>> On Tue, Aug 9, 2016 at 11:12 PM, /#!/JoePea <[email protected]> wrote: >>>>>> >>>>>>> I can get the whole thing to work if I pass the C dependency into >>>>>>> the `setUpA` and `setUpB` functions as follows, but oddly `A` is >>>>>>> `undefined` in the Entrypoint module at the `console.log` statement, >>>>>>> which >>>>>>> makes it seem to me like live bindings aren't working the I was >>>>>>> expecting. >>>>>>> >>>>>>> ```js >>>>>>> // --- Entrypoint >>>>>>> >>>>>>> import A from './app/A' >>>>>>> console.log('Entrypoint', A) // HERE, output: "Entrypoint undefined" >>>>>>> ``` >>>>>>> >>>>>>> ```js >>>>>>> // --- Module A >>>>>>> >>>>>>> import C from './C' >>>>>>> >>>>>>> let A >>>>>>> >>>>>>> export >>>>>>> function setUpA(C) { >>>>>>> >>>>>>> console.log('setUpA') >>>>>>> console.log(C) >>>>>>> >>>>>>> A = class A extends C { >>>>>>> // ... >>>>>>> } >>>>>>> >>>>>>> } >>>>>>> >>>>>>> console.log('Module A', C, setUpA) >>>>>>> >>>>>>> export {A as default} >>>>>>> ``` >>>>>>> >>>>>>> ```js >>>>>>> // --- Module B >>>>>>> >>>>>>> import C from './C' >>>>>>> >>>>>>> let B >>>>>>> >>>>>>> export >>>>>>> function setUpB(C) { >>>>>>> >>>>>>> console.log('setUpB', C) >>>>>>> >>>>>>> B = class B extends C { >>>>>>> // ... >>>>>>> } >>>>>>> >>>>>>> } >>>>>>> >>>>>>> console.log('Module B', C, setUpB) >>>>>>> >>>>>>> export {B as default} >>>>>>> ``` >>>>>>> >>>>>>> ```js >>>>>>> // --- Module C >>>>>>> >>>>>>> import A, {setUpA} from './A' >>>>>>> import B, {setUpB} from './B' >>>>>>> >>>>>>> let C = class C { >>>>>>> constructor() { >>>>>>> // this may run later, after all three modules are >>>>>>> evaluated, or >>>>>>> // possibly never. >>>>>>> console.log(A) >>>>>>> console.log(B) >>>>>>> } >>>>>>> } >>>>>>> >>>>>>> setUpA(C) >>>>>>> console.log('Module C', A) >>>>>>> >>>>>>> setUpB(C) >>>>>>> console.log('Module C', B) >>>>>>> >>>>>>> export {C as default} >>>>>>> ``` >>>>>>> >>>>>>> */#!/*JoePea >>>>>>> >>>>>>> On Tue, Aug 9, 2016 at 9:59 PM, /#!/JoePea <[email protected]> wrote: >>>>>>> >>>>>>>> It seems that the environment I'm in (Meteor uses [reify]( >>>>>>>> https://github.com/benjamn/reify)) tries to evaluate A and B >>>>>>>> first, so I thought I could take advantage of "live bindings" by >>>>>>>> changing >>>>>>>> my modules to the following: >>>>>>>> >>>>>>>> ```js >>>>>>>> // --- Entrypoint >>>>>>>> >>>>>>>> import A from './app/A' >>>>>>>> console.log('Entrypoint', A) >>>>>>>> ``` >>>>>>>> >>>>>>>> ```js >>>>>>>> // --- Module A >>>>>>>> >>>>>>>> import C from './C' >>>>>>>> >>>>>>>> let A >>>>>>>> >>>>>>>> export >>>>>>>> function setUpA() { >>>>>>>> >>>>>>>> console.log('setUpA') >>>>>>>> console.log(C) >>>>>>>> >>>>>>>> A = class A extends C { >>>>>>>> // ... >>>>>>>> } >>>>>>>> >>>>>>>> } >>>>>>>> >>>>>>>> console.log('Module A', C, setUpA) >>>>>>>> >>>>>>>> export {A as default} >>>>>>>> ``` >>>>>>>> >>>>>>>> ```js >>>>>>>> // --- Module B >>>>>>>> >>>>>>>> import C from './C' >>>>>>>> >>>>>>>> let B >>>>>>>> >>>>>>>> export >>>>>>>> function setUpB() { >>>>>>>> >>>>>>>> console.log('setUpB', C) >>>>>>>> >>>>>>>> B = class B extends C { >>>>>>>> // ... >>>>>>>> } >>>>>>>> >>>>>>>> } >>>>>>>> >>>>>>>> console.log('Module B', C, setUpB) >>>>>>>> >>>>>>>> export {B as default} >>>>>>>> ``` >>>>>>>> >>>>>>>> ```js >>>>>>>> // --- Module C >>>>>>>> >>>>>>>> import A, {setUpA} from './A' >>>>>>>> import B, {setUpB} from './B' >>>>>>>> >>>>>>>> let C = class C { >>>>>>>> constructor() { >>>>>>>> // this may run later, after all three modules are >>>>>>>> evaluated, or >>>>>>>> // possibly never. >>>>>>>> console.log(A) >>>>>>>> console.log(B) >>>>>>>> } >>>>>>>> } >>>>>>>> >>>>>>>> setUpA() >>>>>>>> console.log('Module C', A) >>>>>>>> >>>>>>>> setUpB() >>>>>>>> console.log('Module C', B) >>>>>>>> >>>>>>>> export {C as default} >>>>>>>> ``` >>>>>>>> >>>>>>>> As you can see, modules A and B simply export the code that should >>>>>>>> be evaluated (note the live bindings). Then finally, the C module is >>>>>>>> evaluated last. At the end of the C module, you see that it calls >>>>>>>> `setUpA` >>>>>>>> and `setUpB`. When it fires `setUpA`, an error is thrown on the second >>>>>>>> `console.log` that `C` is undefined (or, specifically, `C.default` is >>>>>>>> `undefined` because the ES6 modules are compiled into CommonJS form). >>>>>>>> >>>>>>>> I thought that if `C` was a live binding, then it should be ready >>>>>>>> by the time the `setUpA` function is called. Should this in fact be the >>>>>>>> case? >>>>>>>> >>>>>>>> */#!/*JoePea >>>>>>>> >>>>>>>> On Tue, Aug 9, 2016 at 5:36 PM, John Lenz <[email protected]> >>>>>>>> wrote: >>>>>>>> >>>>>>>>> Without a way to load "later" (aka "soft") dependencies, ES6 >>>>>>>>> module will continue to be more or less broken for circular >>>>>>>>> dependencies. >>>>>>>>> >>>>>>>>> On Tue, Aug 9, 2016 at 4:11 PM, Tab Atkins Jr. < >>>>>>>>> [email protected]> wrote: >>>>>>>>> >>>>>>>>>> On Tue, Aug 9, 2016 at 4:00 PM, /#!/JoePea <[email protected]> >>>>>>>>>> wrote: >>>>>>>>>> > True, and so that's why I'm wondering if the module system can >>>>>>>>>> see that it >>>>>>>>>> > can satisfy all module requirements if it simply evaluates >>>>>>>>>> module C first, >>>>>>>>>> > followed by A or B in any order. It is easy for us humans to >>>>>>>>>> see that. It >>>>>>>>>> > would be nice for the module system to see that as well (I'm >>>>>>>>>> not sure if >>>>>>>>>> > that is spec'd or not). >>>>>>>>>> >>>>>>>>>> That knowledge requires, at minimum, evaluating the rest of each >>>>>>>>>> module, beyond what is expressed in the `import` statements. >>>>>>>>>> That's >>>>>>>>>> assuming there's no dynamic trickery going on that would >>>>>>>>>> invalidate >>>>>>>>>> whatever assumptions it can draw from surface-level analysis. >>>>>>>>>> >>>>>>>>>> Because of this, only the `import` statements are declaratively >>>>>>>>>> available to the module system to work with. Based on that, it >>>>>>>>>> definitely can't make any ordering assumptions; all it knows is >>>>>>>>>> that A >>>>>>>>>> imports C, B imports C, and C imports both A and B, making a >>>>>>>>>> circular >>>>>>>>>> import. >>>>>>>>>> >>>>>>>>>> ~TJ >>>>>>>>>> _______________________________________________ >>>>>>>>>> es-discuss mailing list >>>>>>>>>> [email protected] >>>>>>>>>> https://mail.mozilla.org/listinfo/es-discuss >>>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>> >>>>>>> >>>>>> _______________________________________________ >>>>>> es-discuss mailing list >>>>>> [email protected] >>>>>> https://mail.mozilla.org/listinfo/es-discuss >>>>>> >>>>> >>>> >>> >> >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss >> >> >
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