I've got this React app, its being compiled by babel and bundled by webpack.
in a timetable page TimetableManagePage.js I have this snippet:
nextWeek() {
this.setState({
today: this.state.today.clone().add(1, 'w')
});
this.searchSessions();
}
previousWeek() {
this.setState({
today: this.state.today.clone().subtract(1, 'w')
});
this.searchSessions();
}
searchSessions() {
this.props.actions.searchSessions({
query: {
range: {
when: {
gte: this.state.today.clone().startOf('week').toISOString(),
lte: this.state.today.clone().endOf('week').toISOString()
}
}
}
})
.then(() => this.setState({loading: false}))
.catch(() => this.setState({loading: false}));
}
The idea is, if someone clicks the arrows on this:
It will move to the next or previous week.
The searchSessions runs off the state of today, which the previousWeek and nextWeek update. However, I'm finding that the state isn't updated when the search is ran.
this.props.actions.searchSessions update a redux store state, so will set new props on the component...
Now, I thought that maybe this search actually belongs in the render function, all state should be changed by then... however, any state change in the component will cause the render to be re-run, which means there could be loads of calls to the search, more than there should be.
What is the best way to perform the new search when only the today state is updated? Should I be looking at componentWillUpdate
You should add shouldComponentUpdate(nextState) function and should compare
shouldComponentUpdate(nextState){
if(nextState.today != this.state.today)
return true;
}
then it will only update your page when today state is updated. After that you can call it from componentWillUpdate or whereever you want.
componentWillUpdate(nextState){
if(nextState.today!=this.state.today){
doIt();
}
}
Related
So I have this nuxt page /pages/:id.
In there, I do load the page content with:
content: function(){
return this.$store.state.pages.find(p => p.id === this.$route.params.id)
},
subcontent: function() {
return this.content.subcontent;
}
But I also have an action in this page to delete it. When the user clicks this button, I need to:
call the server and update the state with the result
redirect to the index: /pages
// 1
const serverCall = async () => {
const remainingPages = await mutateApi({
name: 'deletePage',
params: {id}
});
this.$store.dispatch('applications/updateState', remainingPages)
}
// 2
const redirect = () => {
this.$router.push({
path: '/pages'
});
}
Those two actions happen concurrently and I can't orchestrate those correctly:
I get an error TypeError: Cannot read property 'subcontent' of undefined, which means that the page properties are recalculated before the redirect actually happens.
I tried:
await server call then redirect
set a beforeUpdate() in the component hooks to handle redirect if this.content is empty.
delay of 0ms the server call and redirecting first
subcontent: function() {
if (!this.content.subcontent) return redirect();
return this.content.subcontent;
}
None of those worked. In all cases the current page components are recalculated first.
What worked is:
redirect();
setTimeout(() => {
serverCall();
}, 1000);
But it is obviously ugly.
Can anyone help on this?
As you hinted, using a timeout is not a good practice since you don't know how long it will take for the page to be destroyed, and thus you don't know which event will be executed first by the javascript event loop.
A good practice would be to dynamically register a 'destroyed' hook to your page, like so:
methods: {
deletePage() {
this.$once('hook:destroyed', serverCall)
redirect()
},
},
Note: you can also use the 'beforeDestroy' hook and it should work equally fine.
This is the sequence of events occurring:
serverCall() dispatches an update, modifying $store.state.pages.
content (which depends on $store.state.pages) recomputes, but $route.params.id is equal to the ID of the page just deleted, so Array.prototype.find() returns undefined.
subcontent (which depends on content) recomputes, and dereferences the undefined.
One solution is to check for the undefined before dereferencing:
export default {
computed: {
content() {...},
subcontent() {
return this.content?.subcontent
👆
// OR
return this.content && this.content.subcontent
}
}
}
demo
I have a simple h3 tag containing a title that is bound to a reactive data property.
I am fetching the value from a Firestore database and assign it to the data property. When I don't reload and access the page through client-side navigation, everything works fine.
However once I reload the title value gets updated properly (seen in console logs and vue dev tools) but the h3-tag remains empty.
Here is the code:
<template>
<h3 #click="displayCoursePreview" class="mt-5">{{ titl }}</h3>
</template>
<script>
props: {
student: {
type: Boolean
}
},
watch: {
rehydrated: {
// Always triggers once store data is rehydrated (seems to work without any problems)
immediate: true,
async handler(newVal, oldVal) {
if (newVal) {
await this.getSections();
return this.getTopics();
}
}
}
},
data() {
return {
titl: null
};
},
computed: {
rehydrated() {
return this.$store.state.rehydrated; // Equals true once store is rehydrated from local storage
}
},
methods: {
getSections() {
console.log('running') // Runs every time
let ref = this.$store.state.courses;
var cid = this.student
? ref.currentlyStudying.cid
: ref.currentlyPreviewing.cid;
// Get Course Title
this.$fireStore
.collection("courses")
.doc(cid)
.get()
.then(doc => {
console.log(doc.data().name) // Logs correct title every time
this.titl = doc.data().name;
this.thumbSrc = doc.data().imgsrc;
})
.catch(err => console.log(err));
}
</script>
I can't figure out why it sometimes displays the title and sometimes does not. Is there another way to bind titl to the content of the h3-tag without the {{}} syntax?
Thank you in advance!
EDIT:
I have changed the {{}} syntax to v-text like so:
<h3 #click="displayCoursePreview" class="mt-5" v-text="titl"></h3>
And now it works every time, even after a hard reload. Can anyone explain the difference and why this works?
To answer the original question it looks like you might have a race condition between this component and the store. The watch will only trigger 'getSections' if it sees a change in this.$store.state.rehydrated after it's been mounted, but the store might have completed that before this component got mounted, so then the watch never gets triggered.
Not sure why switching to v-text would have altered this, maybe it allows the component to mount slightly faster so it's getting mounted before the store completes it's rehydration?
I have a react app and I am using geolocated to get users location.
Following the instructions for the initialization I have wrapped the component:
export default geolocated({
positionOptions: {
enableHighAccuracy: true,
},
userDecisionTimeout: 15000,
})(ShowPois);
As soon as the user accepts (allows) the location finding on the browser I want two things to happen.
First I need to set a flag when then location is available to the app, so I have this:
static getDerivedStateFromProps(props, state) {
if (!state.geolocatedReady && props.coords) {
return {
geolocatedReady: true
}
}
return null;
}
Notice that props.coords comes from geolocated
The second thing is that I want to complete an input box with the address of the location found. In order to do this I have to do a post request to an api to get the address, but the problem is I cannot use the getDerivedStateFromProps() method because the method must return a value, not a promise (made by axios post request).
So how can I make a post request and then set the state when a prop changes in the component?
getDerivedStateFromProps is only for edge cases. The case you have here sounds like a fit for componentDidUpdate.
componentDidUpdate() {
if(!this.state.geolocatedReady && this.props.coords) {
this.setState({
geolocatedReady: true,
});
this.getAddress(this.props.coords);
}
}
getAddress = async (coords) => {
const address = await mapApi.getAddress(coords);
// or whatever you want with it.
this.setState({
address
})
}
UPDATE: Yes for use case 1, if I extract search.value outside the useEffect and use it as a dependency it works.
But I have an updated Use case below
Use Case 2: I want to pass a searchHits Object to the server. The server in turn return it back to me with an updated value in response.
If I try using the searchHits Object I still get the infinite loop
state: {
visible: true,
loading: false,
search: {
value: “”,
searchHits: {....},
highlight: false,
}
}
let val = search.value
let hits = search.searchHits
useEffect( () => {
axios.post(`/search=${state.search.value}`, {hits: hits}).then( resp => {
…do something or ..do nothing
state.setState( prevState => {
return {
…prevState,
search: {... prevState.search, hits: resp.hit}
}
})
})
}, [val, hits])
Use Case 1: I want to search for a string and then highlight when I get results
e.g.
state: {
visible: true,
loading: false,
search: {
value: “”,
highlight: false,
}
}
useEffect( () => {
axios.get(`/search=${state.search.value}`).then( resp => {
…do something or ..do nothing
state.setState( prevState => {
return {
…prevState,
search: {... prevState.search, highlight: true}
}
})
})
}, [state.search])
In useEffect I make the API call using search.value.
eslint complains that there is a dependency on state.search , it does not recognize state.search.value. Even if you pass state.search.value it complains about state.search
Now if you pass state.search as dependecy it goes in an infinite loop because after the api call we are updating the highlights flag inside search.
Which will trigger another state update and a recursive loop.
One way to avoid this is to not have nested Objects in state or move the highlights flag outside search, but I am trying to not go that route give the sheer dependecies I have.
I would rather have an Object in state called search the way it is. Is there any way to better approach this.
If I want to keep my state Object as above how do I handle the infinite loop
Just a eslint stuff bug may be. You have retracted some code by saying //do something and have hidden he code. Are you sure that it doesn't have anything to do with search object?
Also, try to extract the variable out before useEffect().
const searchValue = state.search.value;
useEffect(()=>{// axios call here},[searchValue])
If your search value is an object, react does shallow comparison and it might not give desired result. Re-rendering on a set of object dependencies isn't ideal. Extract the variables.
React does shallow comparison of dependencies specified in useEffect
eg.,
const {searchParam1, searchParam2} = search.value;
useEffect(() => {
//logic goes here
}, [searchParam1, searchParam2]);
Additionally, you can add dev dependency for eslint-plugin-react-hooks, to identify common errors with hooks
Quick story of my problem:
Absolutely no data is stored in my vuex state when the page loads
If the user is logged in(or has info stored in window.localStorage and therefore gets auto logged in) my vuex store retrieves all the info from a socket that requires authentication.
Then the user logs out, But my vuex state save still retains all its data
This would be a security issue as not logged in people(or hackers) on a public pc could view what the state was before the user logged out.
I have seen How to clear state in vuex store?
But I feel that this is a hack and should be avoided.
My current solution is just to refresh the page using location.reload();
Is there a better way to prevent this data leak?
All objects stored in Vue act as an observable. So if the reference of a value is changed/mutated it triggers the actual value to be changed too.
So, In order to reset the state the initial store modules has to be copied as a value.
On logging out of a user, the same value has to be assigned for each module as a copy.
This can be achieved as follows:
// store.js
// Initial store with modules as an object
export const initialStoreModules = {
user,
recruitment,
};
export default new Vuex.Store({
/**
* Assign the modules to the store
* using lodash deepClone to avoid changing the initial store module values
*/
modules: _.cloneDeep(initialStoreModules),
mutations: {
// reset default state modules by looping around the initialStoreModules
resetState(state) {
_.forOwn(initialStoreModules, (value, key) => {
state[key] = _.cloneDeep(value.state);
});
},
}
});
Then call commit("resetState"); when the user logs out.
Normal Approach
If user logs in, then you can add few boolean flags to ensure that user has been loggedin/loggedout.
So initial approach would be -
this.$store.commit('insertToken', {realtoken, isLoggedIn: true})
In vuex than,
insertToken (state, payload) {
state.token = payload.realtoken
state.isLoggedIn = payload.isLoggedIn
localStorage.setItem('token', payload.realtoken)
}
And when user logs out you should set all flags to false,
In component -
logout () {
this.$store.commit('logOut')
this.$router.replace('/login')
}
and in vuex,
logOut (state, payload) {
state.token = null
state.isLoggedIn = false
localStorage.setItem('token', null)
},
So by means of isLoggedIn and token you can tell router where to navigate by using term called Navigation Guards
Example -
const checkToken = () => {
if ((localStorage.getItem('token') == null) ||
(localStorage.getItem('token') == undefined)) {
return false
} else {
return true
}
}
// Navigation guards
if (to.path === '/') {
if (checkToken()) {
next()
} else {
router.push('/login')
}
}
This is the way I use when authentication is done by means of using token as part of interacting with Vuex.
This extension does a nice job
https://www.npmjs.com/package/vuex-extensions
With it installed I can just call reset in the Vuex Logout Action
logout(context) {
// do the logout stuff, such as
context.commit("setUser", {});
// On logout, clear all State, using vuex-extensions
this.reset();
// if using router, change to login page
router.replace("/login");
}
This might be late but I found window.localStorage.removeItem('vuex') useful. Thanks to Thomas von Deyen, https://github.com/championswimmer/vuex-persist/issues/52#issuecomment-413913598