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React component is re-rendering items removed from state

This is a difficult one to explain so I will do my best!
My Goal
I have been learning React and decided to try build a Todo List App from scratch. I wanted to implement a "push notification" system, which when you say mark a todo as complete it will pop up in the bottom left corner saying for example "walk the dog has been updated". Then after a few seconds or so it will be removed from the UI.
Fairly simple Goal, and for the most part I have got it working... BUT... if you quickly mark a few todos as complete they will get removed from the UI and then get re-rendered back in!
I have tried as many different ways of removing items from state as I can think of and even changing where the component is pulled in etc.
This is probably a noobie question, but I am still learning!
Here is a link to a code sandbox, best way I could think of to show where I am at:
Alert Component State/Parent
https://codesandbox.io/s/runtime-night-h4czf?file=/src/components/layout/PageContainer.js
Alert Component
https://codesandbox.io/s/runtime-night-h4czf?file=/src/components/parts/Alert.js
Any help much appreciated!

When you call a set function to update state, it will update from the last rendered value. If you want it to update from the last set value, you need to pass the update function instead of just the new values.
For instance, you can change your setTodos in your markComplete function to something like this.
setTodos(todos => todos.map((todo) => {
if (id === todo.id) {
todo = {
...todo,
complete: !todo.complete,
};
}
return todo;
}));
https://codesandbox.io/s/jovial-yalow-yd0jz

If asynchronous events are happening, the value in the scope of the executed event handler might be out of date.
When updating lists of values, use the updating method which receives the previous state, for example
setAlerts(previousAlerts => {
const newAlerts = (build new alerts from prev alerts);
return newAlerts;
});
instead of directly using the alerts you got from useState.

In the PageContainer.js, modify this function
const removeAlert = (id) => {
setAlerts(alerts.filter((alert) => alert.id !== id));
};
to this
const removeAlert = (id) => {
setAlerts(prev => prev.filter((alert) => alert.id !== id));
};
This will also fix the issue when unchecking completed todos at high speed

React Redux - quick flash of previous state before dispatch issue

I'm building a React + Redux app with a Node.js backend, and one of the features is that a user can view profiles of other users. To do this, I have a section in the Redux state called users that looks like:
{
...,
users: {
user: {},
isLoading: true
}
}
Every time the /users/:id route is rendered, a getUser(id) action is dispatched and fills the state with the received information.
The main issue is when a user views user1's profile page (therefore redux state is now filled with user1's profile) and then views user2's profile page, the dispatch getUser(2) action is called right after the page is rendered. Since user1's info is still in the state, it will flash their info for a very short time, and then show the loading spinner until the new user is loaded.
I read about dispatching a resetUser(id) action on every unmount of the page, but I'm not sure if this is the right way to go. Also, one of the features is if a user is viewing their own page, they have an edit button which redirects them to /edit-profile. If I reset the state on every unmount, I'll have to fetch their profile again (in the edit page), even though I just did that when they viewed their page.. And that doesn't seem like it makes sense.
Any ideas how to solve this? Thanks!

The render phase runs after mounting. And you stated that previous data is being shown before new data. It seems that you have asynchronous mounting:
async componentDidMount() {}
It will continue rendering even before mounting phase is completed. To avoid issue, you may use synchronous nature of mounting:
componentDidMount(){}
Where you'll call api data.
Now, when you reach to rendering phase it will have new data available before rendering and won't flash you old data.
You now may be wondering how to call api asynchronously. You can create a asynchronous function and call that function inside the synchronous componentDidMount.
componentDidMount() {
yourAsyncFunc()
}
async yourAsyncFunc() {} // api call
How can I do this with React hooks?
While using useEffect, don't implement async:
useEffect(async () =>
Implement it simply:
useEffect(() => {
// you can still use asynchronous function here
async function callApi() {}
callApi()
}, []) // [] to run in similar to componentDidMount
If you miss second parameter to useEffect then you are not ensuring it to run on mounting phase. It will run before, after, and in the rendering phase depending on case.

Implementing something like resetUser(id) seems to be the right way here. I use this approach in my current project and this does solve the problem. The other approach of removing async keyword from useEffect callback as mentioned in another answer didn't work for me (I use hooks, redux-toolkit, Typescript).
After dispatching this action, your state should look something like
{
...,
users: {
user: null,
isLoading: false,
}
}
If you are using hooks, you can dispatch the action this way:
useEffect(() => {
const ac = new AbortController();
...
return () => {
dispatch(resetUser(null));
ac.abort();
};
}, []);
Action could look something like this:
resetListingDetails(state, action) {
// Immer-like mutable update
state.users = {
...state.users,
user: null,
};
}

Electron.js + React/Redux - best practices

So, here the thing.
We have main process and renderer and they`re is isolated from each other and only bridge is IPC messages(to main process) or BrowserWindow webcontents send(to main process).
I'm handling my events in componentDidMount like so:
ipcRenderer.on('deviceWasPlugged', this.deviceWasPluggedListener);
And ofc I'll remove this listener with componentWillUnount for preventing memory leaking in case the component was destroyed:
ipcRenderer.removeListener('deviceWasPlugged', this.deviceWasPluggedListener);
Obviously I have a such method in my Class/Component
deviceWasPluggedListener = (e, somedata) => {
// boring stuff goes there...
}
All is peachy, except one fact - It doesn't seems right as for me.
I still think, there should be a better place to keep my events listeners.
I think, I cant keep it in redux middleware, coz event based model won't allow me to unsubscribe of this events in redux middleware and multiple events will be created when I'll be trying to dispatch smth, even if I'll switch it by action.type:
const someMiddleware = store => next => action => {
if (action.type === 'SOME_TYPE') {
// ...
}
next(action);
};
export default someMiddleware;
So, guys, please tell me is there any better place to keep my backend events? It should be triggered every time I want it, and it shouldn't cause memory leaking problem with maxEventListeners.

Subscriptions with react-meteor-data

From the docs, I wrote my container like so
export default InventoryItemsList = createContainer(() => {
const itemsCollection = Meteor.subscribe('allInventoryItems');
const loading = !itemsCollection.ready();
return {
loading,
items: !loading ? InventoryItems.find().fetch() : []
};
}, class InventoryItemsListComponent extends Component {
render() {
let items = this.props.items;
/* some render logic */
return /*... react component template ...*/ ;
}
});
The problem I see is that
The container function is executed many times, thus calling Meteor.subscribe more than once; is that good? Will Meteor just ignore subsequent subscriptions?
According to this tutorial, subscriptions need to be stopped, but the docs do not mention it at all. This does not take care on it's own, does it?
What is the recommended way to stop (i.e. unsubscribe) or resolve the 2 issues that I see from that point?
Is TrackerRact actually better? (yes, I know this is opinionated, but surely there is some form of a convention with meteor react, here!)

1) The container component is a reactive component, so whenever documents are changed or added to the given collection, it's going to call via your container and update the DOM.
2) As far as I know, the container will only subscribe to the collection via the actual component you bind it to. Once you leave that component, the subscriptions should stop.
If you want to unsubscribe directly, you can just call this.props.items.stop() in your componentWillUnmount() method.
Finally, I will have to say that using React specific implementations are always better than using Meteor specific functions (i.e. it's always better to use state variables over Sessions with React, as it's always better to use containers than Tracker.autorun() with React, etc, etc).

About your problem 2), this is how I solve it
1- When you subscribe to something, store those subscriptions references and pass them to the component.
Here an example with 2 subscriptions, but subscribing to only 1, is even easier.
createContainer((props) =>{
const subscription = Meteor.subscribe('Publication1', props.param1);
const subscription2 = Meteor.subscribe('Publication2', props.param1, props.param2);
const loading = !(subscription.ready() && subscription2.ready());
const results1 = loading ? undefined : Collection1.find().fetch();
const results2 = loading ? undefined : Collection2.findOne({a:1});
return {subscriptions: [subscription, subscription2], loading, results1, results2};
}, MyComp);
Then in my component:
class MyComp extends Component {
......
componentWillUnmount() {
this.props.subscriptions.forEach((s) =>{
s.stop();
});
}
....
}
This way, the component will get in props.subscriptions all the subscriptions it needs to stop before unmounting.
Also you can use this.props.loading to know if the subscriptions are ready (of course, you can have 2 different ready1 and ready2 if it helps).
Last thing, after subscribing, if you .find(), dont forget to .fetch(), else the results will not be reactive.

How to show a loading indicator in React Redux app while fetching the data? [closed]

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I'm new to React/Redux. I use a fetch api middleware in Redux app to process the APIs. It's (redux-api-middleware). I think it's the good way to process async api actions. But I find some cases which can't be resolve by myself.
As the homepage (Lifecycle) say, a fetch API lifecycle begins with dispatching a CALL_API action ends with dispatching a FSA action.
So my first case is showing/hiding a preloader when fetching APIs. The middleware will dispatch a FSA action at the beginning and dispatch a FSA action at the end. Both the actions are received by reducers which should be only doing some normal data processing. No UI operations, no more operations. Maybe I should save the processing status in state then render them when store updating.
But how to do this? A react component flow over the whole page? what happen with store updating from other actions? I mean they are more like events than state!
Even a worse case, what should I do when I have to use the native confirm dialog or alert dialog in redux/react apps? Where should they be put, actions or reducers?
Best wishes! Wish for replying.

I mean they are more like events than state!
I would not say so. I think loading indicators are a great case of UI that is easily described as a function of state: in this case, of a boolean variable. While this answer is correct, I would like to provide some code to go along with it.
In the async example in Redux repo, reducer updates a field called isFetching:
case REQUEST_POSTS:
return Object.assign({}, state, {
isFetching: true,
didInvalidate: false
})
case RECEIVE_POSTS:
return Object.assign({}, state, {
isFetching: false,
didInvalidate: false,
items: action.posts,
lastUpdated: action.receivedAt
The component uses connect() from React Redux to subscribe to the store’s state and returns isFetching as part of the mapStateToProps() return value so it is available in the connected component’s props:
function mapStateToProps(state) {
const { selectedReddit, postsByReddit } = state
const {
isFetching,
lastUpdated,
items: posts
} = postsByReddit[selectedReddit] || {
isFetching: true,
items: []
}
return {
selectedReddit,
posts,
isFetching,
lastUpdated
}
}
Finally, the component uses isFetching prop in the render() function to render a “Loading...” label (which could conceivably be a spinner instead):
{isEmpty
? (isFetching ? <h2>Loading...</h2> : <h2>Empty.</h2>)
: <div style={{ opacity: isFetching ? 0.5 : 1 }}>
<Posts posts={posts} />
</div>
}
Even a worse case, what should I do when I have to use the native confirm dialog or alert dialog in redux/react apps? Where should they be put, actions or reducers?
Any side effects (and showing a dialog is most certainly a side effect) do not belong in reducers. Think of reducers as passive “builders of state”. They don’t really “do” things.
If you wish to show an alert, either do this from a component before dispatching an action, or do this from an action creator. By the time an action is dispatched, it is too late to perform side effects in response to it.
For every rule, there is an exception. Sometimes your side effect logic is so complicated you actually want to couple them either to specific action types or to specific reducers. In this case check out advanced projects like Redux Saga and Redux Loop. Only do this when you are comfortable with vanilla Redux and have a real problem of scattered side effects you’d like to make more manageable.

Great answer Dan Abramov!
Just want to add that I was doing more or less exactly that in one of my apps (keeping isFetching as a boolean) and ended up having to make it an integer (which ends up reading as the number of outstanding requests) to support multiple simultaneous requests.
with boolean:
request 1 starts -> spinner on -> request 2 starts -> request 1 ends -> spinner off -> request 2 ends
with integer:
request 1 starts -> spinner on -> request 2 starts -> request 1 ends -> request 2 ends -> spinner off
case REQUEST_POSTS:
return Object.assign({}, state, {
isFetching: state.isFetching + 1,
didInvalidate: false
})
case RECEIVE_POSTS:
return Object.assign({}, state, {
isFetching: state.isFetching - 1,
didInvalidate: false,
items: action.posts,
lastUpdated: action.receivedAt

I'd like to add something. The real world example uses a field isFetching in the store to represent when a collection of items is being fetched. Any collection is generalized to a pagination reducer that can be connected to your components to track the state and show if a collection is loading.
It happened to me that I wanted to fetch details for an specific entity that doesn't fit in the pagination pattern. I wanted to have a state representing if the details are being fetched from the server but also I didn't want to have a reducer just for that.
To solve this I added another generic reducer called fetching. It works in a similar fashion to the pagination reducer and it's responsibility is just to watch a set of actions and generate new state with pairs [entity, isFetching]. That allows to connect the reducer to any component and to know if the app is currently fetching data not just for a collection but for an specific entity.

I didn't happen upon this question until now, but since no answer is accepted I'll throw in my hat. I wrote a tool for this very job: react-loader-factory. It's got slightly more going on than Abramov's solution, but is more modular and convenient, since I didn't want to have to think after I wrote it.
There are four big pieces:
Factory pattern: This allows you to quickly call the same function to set up which states mean "Loading" for your component, and which actions to dispatch. (This assumes that the component is responsible for starting the actions it waits on.) const loaderWrapper = loaderFactory(actionsList, monitoredStates);
Wrapper: The component the Factory produces is a "higher order component" (like what connect() returns in Redux), so that you can just bolt it onto your existing stuff. const LoadingChild = loaderWrapper(ChildComponent);
Action/Reducer interaction: The wrapper checks to see if a reducer it's plugged into contains keywords that tell it not to pass through to the component that needs data. The actions dispatched by the wrapper are expected to produce the associated keywords (the way redux-api-middleware dispatches ACTION_SUCCESS and ACTION_REQUEST, for example). (You could dispatch actions elsewhere and just monitor from the wrapper if you wanted, of course.)
Throbber: The component you want to appear while the data your component depends on isn't ready. I added a little div in there so you can test it out without having to rig it up.
The module itself is independent of redux-api-middleware, but that's what I use it with, so here's some sample code from the README:
A component with a Loader wrapping it:
import React from 'react';
import { myAsyncAction } from '../actions';
import loaderFactory from 'react-loader-factory';
import ChildComponent from './ChildComponent';
const actionsList = [myAsyncAction()];
const monitoredStates = ['ASYNC_REQUEST'];
const loaderWrapper = loaderFactory(actionsList, monitoredStates);
const LoadingChild = loaderWrapper(ChildComponent);
const containingComponent = props => {
// Do whatever you need to do with your usual containing component
const childProps = { someProps: 'props' };
return <LoadingChild { ...childProps } />;
}
A reducer for the Loader to monitor (although you can wire it differently if you want):
export function activeRequests(state = [], action) {
const newState = state.slice();
// regex that tests for an API action string ending with _REQUEST
const reqReg = new RegExp(/^[A-Z]+\_REQUEST$/g);
// regex that tests for a API action string ending with _SUCCESS
const sucReg = new RegExp(/^[A-Z]+\_SUCCESS$/g);
// if a _REQUEST comes in, add it to the activeRequests list
if (reqReg.test(action.type)) {
newState.push(action.type);
}
// if a _SUCCESS comes in, delete its corresponding _REQUEST
if (sucReg.test(action.type)) {
const reqType = action.type.split('_')[0].concat('_REQUEST');
const deleteInd = state.indexOf(reqType);
if (deleteInd !== -1) {
newState.splice(deleteInd, 1);
}
}
return newState;
}
I expect in the near future I'll add things like timeout and error to the module, but the pattern's not going to be very different.
The short answer to your question is:
Tie rendering to rendering code--use a wrapper around the component you need to render with the data like the one I showed above.
Add a reducer that makes the status of requests around the app you might care about easily digestible, so you don't have to think too hard about what is happening.
Events and state aren't really different.
The rest of your intuitions seem correct to me.

Am I the only one thinking that loading indicators don't belong in a Redux store? I mean, I don't think it's part of an application's state per se..
Now, I work with Angular2, and what I do is that I have a "Loading" service which exposes different loading indicators via RxJS BehaviourSubjects.. I guess the mechanism is the same, I just don't store the information in Redux.
Users of the LoadingService just subscribe to those events they want to listen to..
My Redux action creators call the LoadingService whenever things need to change. UX components subscribe to the exposed observables...

You can add change listeners to your stores, using either connect() from React Redux or the low-level store.subscribe() method. You should have the loading indicator in your store, which the store change handler can then check and update the component state. The component then renders the preloader if needed, based on the state.
alert and confirm shouldn't be a problem. They are blocking and alert doesn't even take any input from the user. With confirm, you can set state based on what the user has clicked if the user choice should affect component rendering. If not, you can store the choice as component member variable for later use.

We have three types of notifications in our app, all of which are designed as aspects:
Loading indicator (modal or non-modal based on prop)
Error Popup (modal)
Notification snackbar (non-modal, self closing)
All three of these are at the top level of our app (Main), and wired through Redux as shown in the below code snippet. These props control display of their corresponding aspects.
I designed a proxy that handles all our API calls, thus all isFetching and (api) errors are mediated with actionCreators I import in the proxy. (As an aside, I also use webpack to inject a mock of the backing service for dev so we can work without server dependencies.)
Any other place in the app that needs to provide any type of notification simply imports the appropriate action. Snackbar & Error have params for messages to be displayed.
#connect(
// map state to props
state => ({
isFetching :state.main.get('isFetching'), // ProgressIndicator
notification :state.main.get('notification'), // Snackbar
error :state.main.get('error') // ErrorPopup
}),
// mapDispatchToProps
(dispatch) => { return {
actions: bindActionCreators(actionCreators, dispatch)
}}
)
export default class Main extends React.Component{

I'm saving the urls such as::
isFetching: {
/api/posts/1: true,
api/posts/3: false,
api/search?q=322: true,
}
And then I have a memorised selector (via reselect).
const getIsFetching = createSelector(
state => state.isFetching,
items => items => Object.keys(items).filter(item => items[item] === true).length > 0 ? true : false
);
To make the url unique in case of POST, I pass some variable as query.
And where I want to show an indicator, I simply use the getFetchCount variable