Introduction
I'm using Redux Toolkit to add Redux support to a React application served by a Django app. We're using Typescript, and so we're following the Typescript Quick Start from the Redux Toolkit docs.
An important element of using Redux (Toolkit?) with Typescript is to ensure that your dispatch(...) method has the correct type signature. As described in the docs, if you simply use the useDispatch(...) hook from react-redux,
the default Dispatch type does not know about thunks. In order to correctly dispatch thunks, you need to use the specific customized AppDispatch type from the store that includes the thunk middleware types, and use that with useDispatch. Adding a pre-typed useDispatch hook keeps you from forgetting to import AppDispatch where it's needed.
That's fine, and I followed those instructions. My code exports a new hook, just like the tutorial:
export type AppDispatch = typeof store.dispatch;
export const useAppDispatch = () => useDispatch<AppDispatch>();
My problem is: when I use that hook, the type signature for the dispatch(...) method still doesn't accept thunks. The following code:
const dispatch = useAppDispatch();
dispatch(customAction({ ... params ... }));
Produces a compilation error:
ERROR in [at-loader] ./src/components/Widget.tsx:45:9
TS2345: Argument of type 'AsyncThunkAction<void, CustomActionParams, {}>' is not assignable to parameter of type 'AnyAction'.
Property 'type' is missing in type 'AsyncThunkAction<void, CustomActionParams, {}>' but required in type 'AnyAction'.
My question: Why isn't the typed dispatch method correctly accepting AsyncThunkActions?
Things I've Tried
Interestingly, calling dispatch(...) with the AppDispatch type explicitly parameterized results in the same error. Only parameterizing dispatch(...) with any silences the error, which obviously isn't ideal.
const dispatch = useAppDispatch();
dispatch<AppDispatch>(customAction({ ... params ... })); // same error
dispatch<any>(customAction({ ... params ... })); // error silenced
This makes me think that the issue is AppDispatch not correctly inferring that it should take AsyncThunkAction types, which should happen automatically. Something that could be causing this is that my async action is defined within extraReducers, like so:
export const customAction = createAsyncThunk(
"slice/customAction",
async (payload: CustomActionParams) { ... }
);
export const slice = createSlice({
name: "slice",
initialState,
reducers: {},
extraReducers: (builder) => {
builder.addCase(customAction.fulfilled, (state, action) => { ... });
}
});
I'm not sure why this wouldn't cause the type to update, but it's something I've got to resolve.
Differences from standard setup
A few things about my environment could also theoretically contribute to this issue, so I'm including them here for correctness:
This React application is not a single page application, but is embedded in a rendered Django template by using django-react-templatetags. This library automatically injects script tags inline to pass component props and initialize components using ReactDOM. See this page for an example on how this works.
This means that each component has its own <Provider> component, instead of one <Provider> at the root, but all share the same store.
The useAppDispatch(...) custom method is defined in my store file (store.ts) rather than a hooks.ts at the root, but that shouldn't cause any issues.
Edit: All of this is in a Yarn 2 Workspace, rather than the root directory of a package.
Questions that are not duplicates:
This question uses an incorrect definition for useAppDispatch(...). I'm using the correct definition in my code.
This question doesn't use a custom dispatch hook.
This question uses incorrect and overspecified types for the dispatch method of the thunkAPI object in the payloadCreator method of createAsyncThunk, which I don't currently use. I'm trying to use dispatch as imported via hook in a component, not in my payloadCreator method.
This issue was ultimately caused by some sort of version mismatch between the react-redux and #reduxjs/toolkit packages. I removed my yarn.lock and deleted my node_modules, and reinstalled from scratch, and the issue disappeared!
(Additionally, I also had to pin TypeScript at ~4.1.5 due to a separate issue installing TypeScript with Yarn 2.)
Our company produces an automation framework that is written in svelte/sapper. One feature is that developers can create custom ui widgets, currently using plain js/html/css and our client side api. These widgets are stored in the database and not on the file system.
I think it would be a big plus to allow them to create widgets as svelte components since it contains all of the markup, js and css in one location and would give them all of the benefits of svelte's reactivity.
I have gotten as far as creating an endpoint that compiles components using svelte's server API but that just seems to generate a module that is ready for rollup-plugin-svelte/sapper/babel to finish the job of producing something the browser can use.
How can I manually compile a svelte component down to the final javascript and css that sapper/svelte produces.
Ouch, tough one. Hang tight.
What you're missing actually is the "linking", that is resolving import statements in the compiled code to something the browser can use. This is the work that is typically done by the bundler (e.g. Rollup, Webpack...).
These imports can come from user (widget developer) code. For example:
import { onMount } from 'svelte'
import { readable } from 'svelte/store'
import { fade } from 'svelte/transition'
import Foo from './Foo.svelte'
Or they can be injected by the compiler, depending on the features that are used in your component. For example:
// those ones are inescapable (bellow is just an example, you'll
// get different imports depending on what the compiled component
// actually does / uses)
import {
SvelteComponent,
detach,
element,
init,
insert,
noop,
safe_not_equal,
} from 'svelte/internal'
Svelte compiles .svelte to .js and, optionally, .css, but it doesn't do anything with imports in your code. On the contrary, it adds some (but still, doesn't resolve them, it's out of its scope).
You'd need to parse the compiled code to find those imports that, raw from the compiler, probably points to paths on your file system and your node_modules directory, and rewrite them to something that makes sense for the browser -- that is, URLs...
Doesn't seem much fun, does it? (Or too much of it, depending on how you see things...) Fortunately, you're not alone with this need and we've got pretty powerful tooling dedicated precisely to this task: enter the bundler!
Solving the linking problem
One relatively straightforward approach to this problem (more to come, don't get too excited too early) is to compile your widgets, not with Svelte's compiler API, but with Rollup and the Svelte plugin.
The Svelte plugin essentially does what you were doing with the compiler API, but Rollup will also do all the hard work of rewiring imports and dependencies in order to produce a neat little package (bundle) that is consumable by the browser (i.e. that doesn't rely on your file system).
You can compile one widget (here Foo.svelte) using some Rollup config like this:
rollup.config.Foo.js
import svelte from 'rollup-plugin-svelte'
import commonjs from '#rollup/plugin-commonjs'
import resolve from '#rollup/plugin-node-resolve'
import css from 'rollup-plugin-css-only'
import { terser } from 'rollup-plugin-terser'
const production = !process.env.ROLLUP_WATCH
// include CSS in component's JS for ease of use
//
// set to true to get separate CSS for the component (but then,
// you'll need to inject it yourself at runtime somehow)
//
const emitCss = false
const cmp = 'Foo'
export default {
// our widget as input
input: `widgets/${cmp}.svelte`,
output: {
format: 'es',
file: `public/build/widgets/${cmp}.js`,
sourcemap: true,
},
// usual plugins for Svelte... customize as needed
plugins: [
svelte({
emitCss,
compilerOptions: {
dev: !production,
},
}),
emitCss && css({ output: `${cmp}.css` }),
resolve({
browser: true,
dedupe: ['svelte'],
}),
commonjs(),
production && terser(),
],
}
Nothing very extraordinary here... This is basically the config from the official Svelte template for Rollup, minus the parts pertaining to the dev server.
Use the above config with a command like this:
rollup --config rollup.config.Foo.js
And you'll get your browser-ready compiled Foo widget in public/build/Foo.js!
Rollup also has a JS API so you could run this programmatically as needed from a web server or whatever.
Then you'll be able to dynamically import and then use this module with something like this in your app:
const widget = 'Foo'
const url = `/build/widgets/${widget}.js`
const { default: WidgetComponent } = await import(url)
const cmp = new WidgetComponent({ target, props })
Dynamic imports will probably be necessary in your case, because you won't know about the widgets at the time you build your main app -- hence you will need to construct the import URLs dynamically like above at runtime. Note that the fact that the import URL is a dynamic string will prevent Rollup from trying to resolve it at bundle time. This means the import will end up as written above in the browser, and that it must be an URL (not a file path on your machine) that the browser will be able to resolve.
That's because we're consuming the compiled widget with a browser native dynamic import that we need to set output.format to es in the Rollup config. The Svelte component will be exposed with export default ... syntax, that modern browsers natively understand.
Dynamic imports are very well supported by current browsers. The notable exception is the "old" Edge (before it essentially became Chrome). If you need to support older browsers, polyfills are available (many of them actually -- e.g. dimport).
This config can be further automatized to be able to compile any widget, not just Foo. For example, like this:
rollup.config.widget.js
... // same as above essentially
// using Rollup's --configXxx feature to dynamically generate config
export default ({ configWidget: cmp }) => ({
input: `widgets/${cmp}.svelte`,
output: {
...
file: `public/build/widgets/${cmp}.js`,
},
...
})
You can then use it like this:
rollup --config rollup.config.widget.js --configTarget Bar
We're making progress, yet there remains a few caveats and hurdles to be aware of (and maybe optimize further -- your call).
Caveat: shared dependencies
The above approach should give you the compiled code for your widgets, that you can run in the browser, with no unresolved imports. Good. However, it does so by resolving all dependencies of a given widget when it is built, and bundling all these dependencies in the same file.
Said otherwise, all dependencies that are shared between multiple widgets will be duplicated for every widget, very notably the Svelte dependencies (i.e. imports from svelte or svelte/*). This is not all bad, because it gives you very standalone widgets... Unfortunately, this also add some weight to your widgets code. We're talking something like maybe 20-30 kb of JS added to each widgets that could be shared between all of them.
Also, as we will see soon, having independent copies of Svelte internals in your app has some drawbacks we need to take into consideration...
One easy way to extract common dependencies so they can be shared instead of duplicated is to bundle all your widgets in one pass. This might not be practicable for all the widgets of all your users, but maybe it can be doable at individual user level?
Anyway, here's the general idea. You would change the above Rollup configs to something like this:
rollup.config.widget-all.js
...
export default {
input: ['widgets/Foo.svelte', 'widgets/Bar.svelte', ...],
output: {
format: 'es',
dir: 'public/build/widgets',
},
...
}
We're passing an array of files, instead of just one, as the input (you would probably automatize this step by listing files in a given directory), and we're changing output.file to output.dir, since now we're gonna have several files generated at once. Those files will include common dependencies of your widgets that Rollup will have extracted, and that all your widgets will share between them for reuse.
Further perspectives
It would be possible to push even further, by extracting some shared dependencies (say, Svelte...) yourself and make them available as URLs to the browser (i.e. serve them with your web server). This way, you could rewrite those imports in your compiled code to those known URLs instead of relying on Rollup to resolve them.
This would reduce code duplication entirely, saving weight, and also this would allow to have a single version of those dependencies shared among all the widget that use them. Doing so would also relieve the need to build all widgets that share dependencies in one go at the same time, which is alluring... However, this would be pretty (!) complicated to setup, and you would actually hit diminishing returns fast.
In effect, when you're bundling a bunch of widgets together (or even just one) and let Rollup extract the dependencies, it is possible for the bundler to know what parts of the dependencies are actually needed by the consuming code and skip the rest (keep in mind: Rollup was built with tree shaking as one -- if not the one -- of its main priority, and Svelte was built by the same guy -- meaning: you can expect Svelte to be very tree shaking friendly!). On the other hand, if you extract some dependencies manually yourself: it relieves the need to bundle all consuming code at once, but you will have to expose the whole of the consumed dependencies, because you won't be able to know in advance the parts from them that will be needed.
It's a balance you need to find between what is efficient and what is practical, accounting for the added complexity of each solution to your setup. Given your use case, my own feeling is that the sweet spot is either bundling each widget entirely independently, or bundling a bunch of widgets from, say, the same user together to save some weight, as described above. Pushing harder would probably be an interesting technical challenge, but it would reap just little extra benefits, but somewhat exploding complexity...
OK so we now know how to bundle our widgets for the browser. We even have some degree of control on how to pack our widgets entirely standalone, or take on some extra infrastructure complexity to rather share dependencies between them and save some weight. Now, we've got a special dependency to consider, when we decide how we make our pretty little packets (err, bundles): that's Svelte itself...
Mind the trap: Svelte can't be duplicated
So we understand that when we're bundling a single widget with Rollup, all of its dependencies will be included in the "bundle" (just the one widget file in this case). If you bundle 2 widgets in this way and they share some dependencies, those dependencies will be duplicated in each of those bundles. In particular, you'd get 2 copies of Svelte, one in each widget. Likewise, the dependencies of your "main" app that are shared with some widgets will nonetheless be duplicated in the browser. You'll have multiple copies of the same code that will be used by those different bundles -- your app, different widgets...
However, there is something special about Svelte that you need to know: it doesn't support being duplicated. The svelte/internal module is stateful, it contains some global variables that would be duplicated if you have multiple copies of this code (see above). What this means, in practice, is that Svelte components that don't use the same copie of Svelte internals can't be used together.
For example, if you have a App.svelte component (your main app) and a Foo.svelte component (e.g. a user widget) that have been bundled independently, then you can't use Foo in App, or you'd get weird bugs.
This wouldn't work:
App.svelte
<script>
// as we've seen, in real life, this would surely be a
// dynamic import but whatever, you get the idea
import Foo from '/build/widgets/Foo.js'
</script>
<!-- NO -->
<Foo />
<!-- NO -->
<svelte:component this={Foo} />
That's also the reason why you have this dedupe: ['svelte'] option in the official Svelte template's Rollup config... This is intended to prevent bundling different copies of Svelte, which would happen if you ever used linked packages, for example.
Anyway, in your case it is kind of unescapable to end up with multiple copies of Svelte in the browser, since you're probably not wanting to rebuild your whole main app anytime a user adds or changes one of their widget... Except going to great lengths to extract, centralize, and rewrite the Svelte imports yourself; but, as I said, I don't believe this would be a reasonable and sustainable approach.
And so we're stuck.
Or are we?
The problem of duplicated Svelte copies only occurs when the conflicting components are part of the same components tree. That is, when you let Svelte create and manage the component instances, like above. The problem doesn't exist when you create and manage the component instances yourself.
...
const foo = new Foo({ target: document.querySelector('#foo') })
const bar = new Bar({ target: document.querySelector('#bar') })
Here foo and bar will be entirely independent component trees, as far as Svelte is concerned. Code like this will always work, irrelevantly of how and when (and with which Svelte version, etc.) Foo and Bar were compiled and bundled.
As I understand your use case, this is not a major hurdle. You won't be able to embed your users' widgets into your main app with something like <svelte:component />... However, nothing prevents you from creating and managing the widget instances in the right place yourself. You can create a wrapper component (in your main app) to generalize this approach. Something like this:
Widget.svelte
<script>
import { onDestroy } from 'svelte'
let component
export { component as this }
let target
let cmp
const create = () => {
cmp = new component({
target,
props: $$restProps,
})
}
const cleanup = () => {
if (!cmp) return
cmp.$destroy()
cmp = null
}
$: if (component && target) {
cleanup()
create()
}
$: if (cmp) {
cmp.$set($$restProps)
}
onDestroy(cleanup)
</script>
<div bind:this={target} />
We create a target DOM element from our main app, render an "external" component in it, pass down all the props (we're proxying reactivity), and don't forget to cleanup when our proxy component is destroyed.
The main limitation of such an approach is that Svelte context (setContext / getContext) of the app won't be visible to the proxied components.
Once again, this doesn't really seem like a problem in the widget use case -- maybe even better: do we really want the widgets to have access to every bits of the surrounding app? If really needed, you can always pass bits of context down to the widget components via props.
The above Widget proxy component would then be used like this in your main app:
<script>
import Widget from './Widget.svelte'
const widgetName = 'Foo'
let widget
import(`/build/widgets/${widgetName}.js`)
.then(module => {
widget = module.default
})
.catch(err => {
console.error(`Failed to load ${widgetName}`, err)
})
</script>
{#if widget}
<Widget this={widget} prop="Foo" otherProp="Bar" />
{/if}
And... Here we are? Let's sum it up!
Summary
Compile your widgets with Rollup, not Svelte compiler directly, to produce browser ready bundles.
Find the right balance between simplicity, duplication and extra weight.
Use dynamic imports to consume your widgets, that will be built independently of your main app, in the browser.
Do not try to mix together components that don't use the same copy of Svelte (essentially means bundled together, except if you've launched into some extraordinary hack). It might looks like it works at first, but it won't.
Thanks to the detailed post by #rixo I was able to get this working. I basically created a rollup.widget.js like this:
import json from '#rollup/plugin-json';
import resolve from '#rollup/plugin-node-resolve';
import commonjs from '#rollup/plugin-commonjs';
import svelte from 'rollup-plugin-svelte';
import path from "path";
import fs from "fs";
let basePath = path.join(__dirname,'../widgets');
let srcFiles = fs.readdirSync(basePath).filter(f=>path.extname(f) === '.svelte').map(m=> path.join(basePath,m ));
export default {
input: srcFiles,
output: {
format: 'es',
dir: basePath,
sourcemap: true,
},
plugins: [
json(),
svelte({
emitCss: false,
compilerOptions: {
dev: false,
},
}),
resolve({
browser: true,
dedupe: ['svelte']
}),
commonjs()
]
}
Then generate the svelte components from the database and compile:
const loadConfigFile = require('rollup/dist/loadConfigFile');
function compile(widgets){
return new Promise(function(resolve, reject){
let basePath = path.join(__dirname,'../widgets');
if (!fs.existsSync(basePath)){
fs.mkdirSync(basePath);
}
for (let w of widgets){
if (w.config.source){
let srcFile = path.join(basePath,w.name + '.svelte');
fs.writeFileSync(srcFile,w.config.source);
console.log('writing widget source file:', srcFile)
}
}
//ripped off directly from the rollup docs
loadConfigFile(path.resolve(__dirname, 'rollup.widgets.js'), { format: 'es' }).then(
async ({ options, warnings }) => {
console.log(`widget warning count: ${warnings.count}`);
warnings.flush();
for (const optionsObj of options) {
const bundle = await rollup(optionsObj);
await Promise.all(optionsObj.output.map(bundle.write));
}
resolve({success: true});
}
).catch(function(x){
reject(x);
})
})
}
And then consume the dynamic widget as #rixo proposed:
<script>
import {onMount, onDestroy, tick} from 'svelte';
import Widget from "../containers/Widget.svelte";
export let title = '';
export let name = '';
export let config = {};
let component;
let target;
$: if (name){
loadComponent().then(f=>{}).catch(x=> console.warn(x.message));
}
onMount(async function () {
console.log('svelte widget mounted');
})
onDestroy(cleanup);
async function cleanup(){
if (component){
console.log('cleaning up svelte widget');
component.$destroy();
component = null;
await tick();
}
}
async function loadComponent(){
await cleanup();
let url = `/widgets/${name}.js?${parseInt(Math.random() * 1000000)}`
let comp = await import(url);
component = new comp.default({
target: target,
props: config.props || {}
})
console.log('loading svelte widget component:', url);
}
</script>
<Widget name={name} title={title} {...config}>
<div bind:this={target} class="svelte-widget-wrapper"></div>
</Widget>
A few notes/observations:
I had much better luck using rollup/dist/loadConfigFile than trying to use rollup.rollup directly.
I went down a rabbit hole of trying to create both client and server globals for all of the svelte modules and marking them as external in the widget rollup so that everything used the same svelte internals. This ended up being a mess and gave the widgets access to more than I wanted.
If you try to embed your dynamically compiled widget in your main app with <svelte:component it will sort of work but give you the dreaded outros.c undefined error if you try to reference a dynamic widget from another. After this happens reality breaks down and the app is in a strange state.
#rixo is always right. I was warned about each of these things in advance and the result was exactly as predicted.
Project (Todolist) was created with immutable library, source here
Store structure: project have many tasks, In redux store: State - map, projects, tasks - Records
When I asyncly remove project ...
export const removeProject = project => (dispatch) => {
if (!isProjectExist(project)) return Promise.resolve()
return projectService
.delete(project)
.then(
() => {
dispatch(remove(project))
console.log("post removeProject resolved")
},
handleError,
)
}
.... that was created after initialization - it will be deleted and properly unmounted, but when project was passed as initialState - ProjectList will not be rerendered, and ProjectItem try to render itself with stale data, and fail, as in picture
It have tests
It looks like reducer returs changed data, but I use immutablejs, and previously i use normalizr-immutable, but I thought that source of issue in this library and write my own normalizeInitialState (source), it did not help, now I think that maybe source of problem in redux-immutable
I struggled entire day on solving of this problem
creator of redux says
I don't think this is something we can fix. React state changes are
asynchronous and React may (or may not) batch them. Therefore, the
moment you press “Remove”, the Redux store updates, and both Item and
App receive the new state. Even if the App state change results in
unmounting of Items, that will happen later than mapStateToProps is
called for Item.
Unless I'm mistaken, there is nothing we can do. You have two options:
Request all required state at App (or a lower, e.g. ItemList) level
and pass it down to “dumb” Items. Add safeguards to mapStateToProps
for “currently unmounting” state. For example, you may return null
from render in this case. Potentially we could have the component
generated by connect() return null from its render if mapStateToProps
returned null. Does this make any sense? Is this too surprising?
Hm, I never saw stubs like return (<div></div>) or safeguards in mapStateToProps in others code
markerikson
I'm not entirely sure I follow what exactly your problem is, but as a
guess: it sounds like the child component is re-rendering before the
parent is. This is a known issue with React-Redux v4 and earlier. The
v5 beta fixes that issue. Try installing react-redux#next and see if
that takes care of your problem.
Let us have two react-redux connects composed with some other higher order components:
export default compose(
connect((state) => {
console.log('In outer connect')
return state
}),
requireAuthState(isLoggedIn, '/'),
connect(
(state) => {
console.log('In inner connect')
return state
},
(dispatch, props) => ({
...
})
),
)(Profile)
I have noticed that if state is changed, the listener related to the inner connect is called first. In this case, the console log would be:
In inner connect
In outer connect
Is this a bug or a feature or one should not assume anything about the order in which react-redux handles re-rendering of connected components?
It is causing problems for me in this particular case. The requireAuthState h.o.c. sometimes (depending on the app state) does not render its children. However, the inner connect tries to re-render anyways, which then results in an error.
Yes, this is a known issue with React-Redux up through v4. The wrapper components subscribe in componentDidMount, which is fired bottom-to-top, so it's quite possible that child components can subscribe before their parents.
The upcoming React-Redux v5 (which will hopefully be released shortly) fixes this issue by enforcing top-down subscriptions, which also helps improve performance. See React-Redux PR #416 for further details, as well as the release notes.
I am building an isomorphic application with code splitting using react router and redux. I have gone about as far as I can, but I need some help to figure out the rest of my problem. I have a large application that requires code splitting for the front end. I have a reducer registry that enables me to register new reducers(lazy loaded), or replace existing reducers in my store. This works great, however because sections of my app are lazy loaded, my lazy loaded reducers are not present when I call combineReducers() on the client side, while they resolve perfectly on the server. This causes an unexpected keys error, and forces my store to ignore the offending key(s) in my initial state.
initialState (from server)
{ "cases": {...}, "user": {...} }
Client side redux expected initialState
This is based off of available reducers
{ "user": {...} }
Loaded Reducer
UserReducer
Lazy Loaded Reducer
CaseReducer
The error occurs when I call the following
const finalCreateStore = compose(
applyMiddleware(promiseMiddleware)
)(createStore);
const rootReducer = combineReducers({...reducers})
const store = finalCreateStore(rootReducer, initialState);
Unexpected key "case" found in initialState argument passed to createStore. Expected to find one of the known reducer keys instead: "user". Unexpected keys will be ignored.
Everything works well on the server, but initializing the app on the client while momentarily missing a reducer until it is loaded is causing this error. Does anyone know how to get around this error, or tell redux to not validate the shape of the initial state? I need "cases" to be available to my lazy loaded reducer.
It seems like you should opt not to use the built-in combineReducers, since you know the warning isn't applicable to your usage. From the Redux guide:
These two ways to write a combined reducer are completely equivalent:
const reducer = combineReducers({
a: doSomethingWithA,
b: processB,
c: c
})
function reducer(state, action) {
return {
a: doSomethingWithA(state.a, action),
b: processB(state.b, action),
c: c(state.c, action)
}
}
So you may as well go with the second option.