Write Stores in Typescript

[Anonyfox]

I couldn't find anything on google, so is this conveniently possible? Basically the bummer for me is that I have to call dispatch/commit with a given identifier string to trigger something.

My vision is to define stores as Typescript classes with typed methods (getting intellisense in editor and so on) which I can call instead of dispatch("my_action", data) and having to look up each and everything and check for errors manually all the time.

Basically my problem is that my team is building a fairly large Vue/Vuex frontend for a core product of our company, consisting of already 18 fairly complex Stores as modules, and this year stuff is going to at least quadruple in size and complexity. We already decided to go on with typescript instead of ES7 and are in the process of migrating our backend/frontend code, but this thing really feels like a bummer.

I think this is not the typical "small" use case for Vue.js, since we're building a huge enterprise frontend with loads of requirements and edge cases, but isn't vuex(/flux) supposed to scale up when complexity rises?

Has anyone experience in building complex, type safe Vuex 2.0 stores in Typescript yet? Any help here would be appreciated

[LinusBorg]

/ping @ktsn

[ktsn]

Thank you for trying Vuex with TypeScript.
Honestly, it is challenge to achieve type safety with pure Vuex API. But we currently can specify action/mutation type as type parameter to let TS compiler can infer the correct type.

// Declare each action type
type ActionA = {
  type: 'A',
  value: number
}

type ActionB = {
  type: 'B',
  value: string
}

// Declare the union type of actions
type Action = ActionA | ActionB

// Provide action type
store.dispatch<Action>({
  type: 'A',
  value: 1
})

About defining the store as class, I believe we can make such binding like vue-class-component and I personally interested in it. Also, there is an experiment for type safety of Vuex. https://github.com/HerringtonDarkholme/kilimanjaro

[Anonyfox]

Mh, okay, this might be a start. For better clarification, I'll provide a simplified example for a store that will later get included as a module:

state.ts:

export class State {
    // persons above 24 years old
    adults: number = 2

    // persons between 16 and 24 years old
    juveniles: number = 0

    // persons below 16 years old
    children: number = 0
}

mutations.ts:

import { State } from './state'

export type personIdentifier = 'adults' | 'juveniles' | 'children'

export class Mutations {
    // increment the chosen persons type by one
    inc (state: State, key: personIdentifier) {
        state[key]++
    }

    // decrement the chosen persons type by one
    dec (state: State, key: personIdentifier) {
        state[key]--
    }
}

actions.ts:

import { Store } from 'vuex'
import { State } from './state'

export class Actions {
    inc ({ commit }: Store<State>) {
        // ??????
    }
}

skipping the getters for now, since they're unimportant. This is where I am currently, and I would combine these classes into a Store with namespaced: true, since this store might be used on multiple places independently for several UI components.

Is there a solution how I might write these actions as type safe methods? Your example is not clear enough for me to apply the pattern you provided, I think.

[ktsn]

Hm, there maybe no solution when namespaced: true is used since we cannot combine string literal type 😞
I guess we need some wrapper to trick the type checking.

[Anonyfox]

small heads-up: it was really straightforward to implement a Store-Module as a standalone npm package in typescript, with tooling/tests/typings and namespaced:true, and then use it dynamically within the core app.

Thanks to the recent efforts of you guys for the typescript support, implementing the interfaces really helped to get it right immediately!

In my opinion the only puzzle-piece left is typesafe commit/dispatch (with namespaced), but I think this is a hard problem to bolt-on vuex as-is. One idea would be to generate types on the "new Vuex.Store" call in the main code, which map the generated identifier-string to the underlying function or sth like that. But ideally, there could be an alternate way to call commit/dispatch, maybe through wrapper classes to Module that does the actual calling behind the scenes or something. This seems to be an architectural issue, which is really not easy to resolve.

On the other hand I think it would really, really great to solve this. Even if approx. most vuex users do "just" use ES7, they could benefit from intellisense/hints from their Editors/IDEs greatly, providing huge ergonomic value once stores become nontrivial in size.

[morhi]

@Anonyfox Would you mind creating an example repository or snippet for vuex with typescript, modules and classes as far as you got it so far? I am currently setting up a vue project which probably will contain a few store modules. I understand using vuex with ES6 but I am struggling with properly setting up my project with typescript. I would like to have everything structured well but it seems a bit complicated at the moment :)

As for now I created two global files (mutations.ts and actions.ts) where I export some constants of the mutation types and actions that all stores use. These files are imported both in the store modules and in the components that use the store so I don't need to use string as identifiers.

[Anonyfox]

@morhi sure, I extracted a simple (but not trivial) store we're using.

https://github.com/Anonyfox/vuex-store-module-example

please respect that I can not give a valid license, this is just intended for demonstrating.

/cc @ktsn

[wonderful-panda]

I think it would be nice if we can use namespaced module like as

/*
 * equivalent to ctx.commit("foo/bar/action", arg)
 */
ctx.commit.foo.bar("action", arg);
// OR
ctx.foo.bar.commit("action", arg);
// OR
ctx.modules.foo.bar.commit("action", arg);

/*
 * equivalent to ctx.getters("foo/bar/prop")
 */
ctx.getters.foo.bar.prop
// OR
ctx.foo.bar.getters.prop
// OR
ctx.modules.foo.bar.getters.prop

This will make adding and combining types more easy.

[morhi]

@Anonyfox wow! thank you very much! I adopted your example into my environment and got it working 👍

[Glidias]

Related: #532

One way to ensure type consnistency between dispatch/commit payload vs. action/mutation handler, is to declare both of them at once. Eg.

http://tinyurl.com/go9ap5u

However, you'd need some sort of runtime decoration approach to setup necessary pre-initializations prior to app running. Also, Typescript doesn't seem to complain if I override a method with a different payload type parameter form, which is something that i'd need to enforce, though (anyway to do this?). Overall, setting up all the decorators and custom initilizations at runtime is a lot of work.

[wonderful-panda]

FYI, I wrote helper to make store half-decent type safe.
https://gist.github.com/wonderful-panda/46c072497f8731a2bde28da40e9ea2d7

It seems to work well except namespaced module.

[Glidias]

@wonderful-panda Is it possible with your code to add modules within modules recursively?

[wonderful-panda]

@Glidias yes.

Nested module example is below:

const module1 = builder.createModule<...>({ /* module1 definition */ });
const module2 = builder.createModule<...>({ /* module2 definition */ });

const parentModule = 
    builder.addModule("bar", module1)
           .addModule("baz", module2)    // { modules: { bar: module1, baz: module2 } }
           .createModule<...>({ /* parentModule definition without `modules` */ });

const store =
    builder.addModule("foo", parentModule)
           .createStore<...>({ /* store options without `modules` */ });

[Glidias]

@wonderful-panda See the comments in the gist for continued discussion in that area.

Regarding dynamic namespacing of modules + strict typing, one idea i was considering is that after a module tree is initialized, you traverse through it's state tree and will always set a _ property under each module state within the tree (including root store state for the sake of homogeneity), in order to have their namespace path references stored dynamically at runtime. That way, you can simply use rootState.moduleA.moduleB._, to retrieve a path accordingly. Or if the context is unknown within actions (may/may not be root), you can use context.state._. However, this will require you to strictly hardcode the module interface field references (under each State for typehinting) if you're not using the builder utility. Also, a _ property reference must be set up as well per module state to ensure you get typehinting/type-completion. The Builder already sets up combined state for module references under a given parent state, so your Module state would probably just implement a dummy IPrefixedState interface that provides an optional readonly _?:string parameter that will give you boilerplate typehinting.

For strictly typed dispatches of module-specific mutations/actions, one way is to adopt a generic helper wrapper method to commit something through a given context (with/without namespace prefixing..)

https://github.com/Glidias/vuex-store-module-example/blob/master/src/util/vuexhelpers.ts

However, this will result in a bit of additional performance overhead of calling the wrapper helper function (remember, there's no inlining in Typescript). But i guess, it's okay and shouldn't be too much of an issue.

 import { MutationTypes } from './mutations';

import * as VuexHelper from "./util/vuexhelpers"
const commitTo = VuexHelper.getCommitToGeneric<MutationTypes>();

// within action handler context (affecting another module somewhere else..)
commitTo(context,"INC", "adults", {root:true}, context.rootState.someModule.anotherNestedModule._)

  // if a particular set of action handlers aren't aware if it's registered under a namespaced:true module or not
  commitTo(context,"INC", "adults", {root:true}, context.state._)

 // or something like this within a Component context:
commitTo(this.$store,"INC", "adults", undefined, $store.state.someModule.anotherNestedModule._)

Also, if your module needs to respond to both namespaced vs non-namespaced mutations/actions, namespaced:true vuex setting won't work well anyway. So, here's a possible approach in userland: https://github.com/Glidias/vuex-store-module-example/wiki/Managing-mixed-namespacings-between-module's-mutations-and-actions