add hasModule API

[FranckFreiburger]

What problem does this feature solve?

When adding/removing modules dynamically, it is sometimes mandatory to know if a module has already been added.

What does the proposed API look like?

Store#hasModule(path)

[nickmessing]

You can wait for Optional Chaining Operator to get into babel and use that instead. Looks like ES Committee likes the idea and is going to be discussed at the next meeting again.

[FranckFreiburger]

I am talking about vuex store modules

[posva]

But if you add or remove modules dynamically, you should be able to add a property like added to the module and set it as you need it.
Why would your code add the same module twice?

[FranckFreiburger]

I try to make any Component to support ssr (not only route components).
These components may use the global store to create their own namespace (module).
On the server side, there is no problem since asyncData() is called only once by component by rendering.
However, on the client-side, the asyncData may be called several times. If the component want to create it's own vuex module in the asyncData, it should check if the module has not been previously registered.

eg. with hypothetical Store#hasModule(path)

export default {
	name: 'Test',
	asyncData: async function({ store, route }) {

		if ( !store.hasModule('testVuexModule') ) {
			
			store.registerModule('test', {
				namespaced: true,
				mutations: {
					'TEST': function(state, value) {
						state.testVal = value;
					}
				}
			})
		}

		store.commit('test/TEST', await api.call(...))

[posva]

I see. Still, adding a custom property to the module should work to check if it has been installed

[FranckFreiburger]

yes, but who holds the reference to the module ?
the store is the only one that is able to do that, no ?

(Furthermore, it is quite common to have foo.add(), foo.remove() and also foo.has(), imagine a world without the javascript in operator ...)

[posva]

This is what I'm saying:

import module from './module'

if (!module.registered) store.registerModule('m', module)
module.registered = true

The has or similar exists in arrays and collection because they're general purpose collections

[FranckFreiburger]

ok, but this will break my progressive app, since this code will also run server-side

[posva]

why?

[FranckFreiburger]

server-side, module.registered will always be true (except the first time of course)

[posva]

Well, isn't that the point? Registering only once?

[FranckFreiburger]

yes

[posva]

@ktsn Does it makes sense to add a module twice?
Vue plugins add a property to know if they have been installed and prevent installing again. We could maybe add that too