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Bad idea to put a dom operation inside a redux reducer?

I have several actions which use the same reducer, and instead of having a dom operation in each of those actions, I want to just add it once inside my shared reducer. I know reducers are to be pure (which the returned data still is), but is this some kind of anti-pattern or an acceptable strategy?
case APPEND_POSTS:
!payload.length &&
document.getElementById('posts-cont').classList.add('no-more-posts'); // this
const total = state.posts.length + payload.length;
const limit = total > posts_to_keep_limit ? 50 : 0;
return {
...state,
posts: [...state.posts.slice(limit), ...payload],
loading: false,
};
```

Redux Action
case APPEND_POSTS:
// you don't need to use below code.
// !payload.length && document.getElementById('posts-cont').classList.add('no-more-posts'); // this
const total = state.posts.length + payload.length;
const limit = total > posts_to_keep_limit ? 50 : 0;
return {
...state,
posts: [...state.posts.slice(limit), ...payload],
nomore: true,
loading: false,
};
Your component.
function YourComp(props){
const state = useSelector(...);
return ( <div id="posts-cont" className={state.nomore ? 'no-more-posts' : ''} > {...}</div>
}

I know reducers are to be pure (which the returned data still is), but is this some kind of anti-pattern or an acceptable strategy?
The returned data is pure, but you've introduced a side-effect in the form of a DOM mutation. Therefore, this reducer is not pure.
This is indeed an anti-pattern because now, the component(s) that render posts-cont items have an invisible coupling to this reducer. It makes your codebase more difficult to read and debug.

jinongun's advice is good: let the className of the component derive its value from the store's state using a selector. AS for the general question
I have several actions which use the same reducer, and instead of
having a dom operation in each of those actions, I want to just add it
once inside my shared reducer.
DON'T EVER make DOM operations inside a reducer.
Don't ever make any operation that is not a pure computation.
But you can create an action creator that always calls a side effect (with Redux-Thunk):
function appendPosts(payload) {
return dispatch => {
mySideEffect()
dispatch({
type: APPEND_POSTS,
payload
})
}
}
function action1(params) {
return dispatch => {
dispatch({
type: ACTION1,
payload: params
})
dispatch(appendPosts(params))
}
}
function action2(params) {
return dispatch => {
dispatch({
type: ACTION2,
payload: params
})
dispatch(appendPosts(params))
}
}
// etc

How to check action payload before state update?

I'm learning redux for my first react-redux application. How do I manage to verify payload value before changing my state ? For example the code below:
todoExample = {name: 'learn redux', author: 'myself'}
wrongTodoExample = {name: 'learn redux'}
dispatch(addTodos({todo: todoExample}))
dispatch(addTodos({todo: wrongTodoExample }))
With the above code, I add 2 todo items to my state but they don't have the same keys.
Is there a way to check the payload value in order to authorize the first addTodos but not the second one in my reducer?
I've searched on the internet but I couldn't find an answer. I'm sorry if my question is redundant.

You can use redux middleware to verify things, that is absolutely one of the intended use cases for middleware. Any middleware can inspect and modify any action going through the pipeline before it reaches the reducers, and even prevent an action from continuing on.
const verifyPayload = store => next => action => {
if (isVerifyPayload(action.payload)) {
return next(action);
} else {
return store.dispatch({ type: 'NOT_AUTHORIZED' })
}
}
const store = createStore(
initialState,
applyMiddleware(verifyPayload)
)

Not so clear about your description about same key, you mean name or author, or other specific keys like code\id.
You can try to validate your todos before dispatch or within the addTodos
function addTodos(payload) {
if (!payload.todo.code) return;
// simply return,
// otherwise throw an error to indicate that your todos miss a specific key
}

You can use a ternary operator in your reducer along with some util function to validate your todo. If the todo is valid, then transform your state to include the new todo, if not return the same state (effectively doing nothing).
const isValidTodo = (todo) => {
//Implement your validations. E.g: A valid todo will have a name and an author
return todo.name && todo.author;
}
const todos = (state = [], action) => {
switch (action.type) {
case 'ADD_TODO':
return isValidTodo(action.payload) ?
[
...state,
{
name: action.payload.name,
author: action.payload.text,
completed: false
}
]
: state
default:
return state
}
}

I've found a solution that suited well my needs and it's TypeScript. Now I have Payload Type wich allow me to define keys that I need in my action.payload without any validation function.
Thanks all for your asnwers.

How to handle vuex store to fetch data from rest api?

I'm using Vuex to handle my application state.
I need to make an Ajax Get request to a rest api and then show some objects list.
I'm dispatching an action that loads this data from the server but then I don't know how to handle it on the component.
Now I have this:
//component.js
created(){
this.$store.dispatch("fetch").then(() => {
this.objs = this.$store.state.objs;
})
}
But I don't think that the assignment of the incoming data to the local property is the correct way to handle store data.
Is there a way to handle this better? Maybe using mapState?
Thanks!

There are many ways you can do it, you must experiment and find the one that fits your approach by yourself. This is what I suggest
{ // the store
state: {
something: ''
},
mutations: {
setSomething (state, something) {
// example of modifying before storing
state.something = String(something)
}
},
actions: {
fetchSomething (store) {
return fetch('/api/something')
.then(data => {
store.commit('setSomething', data.something)
return store.state.something
})
})
}
}
}
{ // your component
created () {
this.$store
.dispatch('fetchSomething')
.then(something => {
this.something = something
})
.catch(error => {
// you got an error!
})
}
}
For better explanations: https://vuex.vuejs.org/en/actions.html
Now, if you're handling the error in the action itself, you can simply call the action and use a computed property referencing the value in the store
{
computed: {
something () { // gets updated automatically
return this.$store.state.something
}
},
created () {
this.$store.dispatch('loadSomething')
}
}

Why Redux returns old state when dispatch action before?

I want to know why when I dispatch action before my console log prints old state.
if I do next:
reducer.js
let initialState = { display: false };
const MyReducer = (state = initialState,action) => {
...
case 'SET_DISPLAY':
return { update(state,{ display : {$set: action.display } }) }
break;
default:
return state;
break;
}
ActionCreator.js
let ActionCreator = {
setDisplay(value) {
return(dispatch,getState) {
dispatch({ type: 'SET_DISPLAY',display: value})
}
}
};
app.js
componentDidMount(){
this.props.dispatch(ActionCreator.setDisplay(true))
// expected : true
console.log(this.props.display)
// prints : false.
}
const mapStateToProps = (state) => {
display : state.display
}
but I can see changes in my redux dev-tools console.
PD I use redux-thunk as Middleware.its just example,all my code seems good and works great,but,its a question.
Why console logs old state instead a new state (its ilogic, if I dispatched an action before call logs) I will apreciate your answers,thanks.

This is because you are using redux-thunk and your dispatch happens aynchronously.
this.props.dispatch(ActionCreator.setDisplay(true)) will not set display true immediately.
Since you are not making a network request or anything async in that action why dont you change the action creator to
let ActionCreator = {
setDisplay(value) {
return { type: 'SET_DISPLAY',display: value};
}
};
Now it will happen synchronously. Also dont put console log immediately after dispatching. As redux updates state, old state is not modified. Instead it creates a new state instance with updated value. This new value will be passed as props to your component via connect of react-redux.
Try printing display in render() method, you will see that it is called twice and second one will display true.

First, I would recommend not to rely on the fact that dispatching an action may be synchronous; design as if everything was asynchronous. When eventually you dispatch an async actions, you will be pleased to have your mindset ready for that.
Second, your action creator return a function (you must be using the thunk middleware), which is why you get this behaviour.
componentDidMount(){
startSomethingAsync();
}
componentDidUpdate(){
if (!this.props.asyncCompleted) return;
if(this.props.asyncResultFn) {
this.props.dispatch({ type: ... value: VALUE_CONDITIONAL_TRUE})
}
else{
this.props.dispatch({ type: ... value: VALUE_CONDITIONAL_FALSE})
}
}

Trouble triggering reactivity on changed Vuex objects

I'm modifying the value of an existing property on an object that is in an array of objects in my Vuex.store. When I update the store, it is not triggering a re-render of my computed property that is accessing the store. If I reset the stored value to an empty array, and then set it again to my new array, it'll trigger the change. But simply updating the property of the array of objects does not trigger a change.
I have tried using Vue.set() like the docs talk about, and that updates the store, but still does not trigger a re-render of the computed property. What am I missing? Using Vue 2.2.4 and Vuex 2.2.0.
//DEBUG: An example of the updated post I'm adding
let myNewScheduledPost = {
id: 1,
name: 'James'
};
this.$store.dispatch('addScheduledPost', post);
//DEBUG: My store
const options = {
state: {
scheduledPosts: [
{ id: 1, name: 'Jimmy'}
],
},
mutations: {
scheduledPosts: (state, scheduledPosts) => {
//This triggers the reactivity/change so my computed property re-renders
//But of course seems the wrong way to do it.
state.scheduledPosts = [];
state.scheduledPosts = scheduledPosts;
//Neither of these two lines triggers my computed property to re-render, even though there is a change in scheduledPosts
state.scheduledPosts = scheduledPosts;
Vue.set(state, 'scheduledPosts', scheduledPosts);
},
},
actions: {
addScheduledPost({ commit, getters }, newScheduledPost) {
let scheduledPosts = getters.scheduledPosts;
const idx = scheduledPosts.findIndex(existingScheduledPost => existingScheduledPost.id === newScheduledPost.id);
//If the post is already in our list, update that post
if (idx > -1) {
scheduledPosts[idx] = newScheduledPost;
} else {
//Otherwise, create a new one
scheduledPosts.push(newScheduledPost);
}
commit('scheduledPosts', scheduledPosts);
//DEBUG: This DOES have the correct updated change - but my component does not see the change/reactivity.
console.log(getters.scheduledPosts);
}
},
getters: {
scheduledPosts: (state) => {
return state.scheduledPosts;
}
}
};
//DEBUG: Inside of my component
computed: {
mySortedPosts()
{
console.log('im being re-rendered!');
return this.$store.getters.scheduledPosts.sort(function() {
//my sorted function
});
}
}

Your problem is if you are wanting to access a portion of the state you don't use a getter https://vuex.vuejs.org/en/state.html.
computed: {
mySortedPosts(){
return this.$store.state.scheduledPosts
}
}
Getters are for computed properties in the store https://vuex.vuejs.org/en/getters.html. So in your case you might create a getter to sort your scheduled posts then name it sortedScheduledPosts and then you can add it to your components computed properties like you are now.
The key thing is your getter needs to have a different name then your state property just like you would in a component.