I have implemented a watch within a Vue component that displays product information. The watch watches the route object of vue-router for a ProductID param to change. When it changes, I want to go get the product details from the back-end API.
To watch the route, I do this in Product.vue:
import { useRoute } from 'vue-router'
export default {
setup() {
const route = useRoute();
async function getProduct(ProductID) {
await axios.get(`/api/product/${ProductID}`).then(..do something here)
}
// fetch the product information when params change
watch(() => route.params.ProductID, async (newID, oldID) => {
await getProduct(newId)
},
//watch options
{
deep: true,
immediate: true
}
)
},
}
The above code works, except that if a user navigates away from Product.vue, for example using the back button to go back to the homepage, the watch is triggered again and tries to make a call to the API using undefined as the ProductID (becaues ProductID param does not exist on the homepage route) e.g. http://localhost:8080/api/product/undefined. This causes an error to be thrown in the app.
Why does the watch trigger when a user has navigated away from Product.vue?
How can this be prevented properly? I can do it using if(newID) { await getProduct(newId) } but it seems counterintuitive to what the watch should be doing anyway.
UPDATE & SOLUTION
Place the following at the top replacing the name for whatever your route is called:
if (route.name !== "YourRouteName") {
return;
}
That will ensure nothing happens if you are not on the route you want to watch.
I ran into the same problem. Instead of watching the current route, use vue-router onBeforeRouteUpdate, which only gets called if the route changed and the same component is reused.
From https://next.router.vuejs.org/guide/advanced/composition-api.html#navigation-guards:
import { onBeforeRouteLeave, onBeforeRouteUpdate } from 'vue-router'
import { ref } from 'vue'
export default {
setup() {
// same as beforeRouteLeave option with no access to `this`
onBeforeRouteLeave((to, from) => {
const answer = window.confirm(
'Do you really want to leave? you have unsaved changes!'
)
// cancel the navigation and stay on the same page
if (!answer) return false
})
const userData = ref()
// same as beforeRouteUpdate option with no access to `this`
onBeforeRouteUpdate(async (to, from) => {
// only fetch the user if the id changed as maybe only the query or the hash changed
if (to.params.id !== from.params.id) {
userData.value = await fetchUser(to.params.id)
}
})
},
}
watch registers the watcher inside an vue-internal, but component-independent object. I think it's a Map. So destroying the component has no effect on the reactivity system.
Just ignore the case where newID is undefined, like you already did. But to prevent wrapping your code in a big if block just use if(newID === undefined)return; at the beginning of your callback. If your ids are always truthy (0 and "" are invalid ids) you can even use if(!newID)return;.
well, in your use case the best approach would be to have a method or function which makes the api call to the server, having watch is not a really good use of it, because it will trigger whenever route changes and you do not want that to happen, what you want is simply get the productID from route and make the api call,
so it can be done with getting the productID in the created or mounted and make the api call!
Related
I am trying to show some dynamic content in my component but somehow useEffect causes a infinite loop.
What can be the problem?
useEffect(() => {
retrieveLocalData('following').then((contacts) => {
setLocalData(JSON.parse(contacts));
});
}, [getLocalData]);
async function retrieveLocalData(key) {
try {
return await AsyncStorage.getItem(key);
} catch (error) {
console.log(error);
}
}
console.log('test'); // infinite
Code: https://codepen.io/eneskul/pen/OJWEgmw
Updated Answer
The infinite loop is a result of the useEffect hook updating the same value that is triggering the hook to run in the first place.
Here's a simple example to illustrate the problem:
const [value, setValue] = useState({ foo: 'bar' });
useEffect(() => {
Promise.resolve('{"foo":"bar"}').then((result) => {
const newValue = JSON.parse(result);
// `newValue` is a new object, even if its content is identical to `value`.
setValue(newValue);
});
}, [value]);
In this example, when value is set, it causes the useEffect hook to execute, which will asynchronously update value with a new object, which will cause the useEffect hook to execute again, and so on. Even though the contents of the objects are identical, the JSON.parse call creates a new object with a new reference.
You can prevent the infinite loop by doing a deep equality check of the two objects before updating the state. Using something like Lodash's isEqual function makes this pretty easy.
useEffect(() => {
Promise.resolve('{"foo":"bar"}').then((result) => {
setValue((prev) => {
const newValue = JSON.parse(result);
// Do a deep comparison and only update state with new object if content is different.
return isEqual(prev, newValue) ? prev : newValue;
});
});
}, [value]);
In this example, the reference to value will only change if the contents of the objects are different.
However, this only explains what the problem is. I'm not sure what the right solution is for your problem, since it's not clear why the component only needs to load data from local storage into state when the state changes, but the state is only updated when it loads from local storage. There seems to be a "chicken or the egg" problem here. It feels like there should be something else that should trigger loading data from local storage into state, other than the data that was just loaded from local storage into state.
Previous Answer
The likely culprit here is getLocalData in the dependency list of the useEffect hook. If that is not a stable reference (i.e. the reference changes on each render), then it will cause the useEffect hook to execute, which will then trigger a state update, which will trigger a render, which will cause useEffect to execute again, which starts the whole thing over again.
In the sample code, it's not clear where getLocalData comes from. Wherever it comes from, you might consider wrapping it with the useCallback hook to create a stable reference. If it's just a typo and meant to be retrieveLocalData, then that is definitely the issue. Because retrieveLocalData is declared inside the component's render function, it will create a new instance of the function (with a new reference) on each render.
I would just move it inside the useEffect hook and eliminate the dependencies.
useEffect(() => {
AsyncStorage.getItem('following')
.then((contacts) => {
setLocalData(JSON.parse(contacts));
})
.catch((error) => {
console.log(error);
});
}, []);
what I am trying to do is:
construct an URL based on props
initially and whenever the URL changes, fetch some data
Since this is asynchronous and I also want to indicate loading, I use this construct:
const pageUrl = computed(() => `/api/${props.foo}/${props.bar}`)
const state = reactive({
page: null,
error: null,
loading: false
})
watchEffect(async () => {
state.loading = true
try {
const resp = await axios.get(pageUrl.value)
state.page = resp.data
} catch (err) {
state.error = err
console.log(err)
}
state.loading = false
})
// return page, loading, error for the component to use
The problem is that this seems to run in an infinite loop because in the body, I am not only reacting to the pageUrl, but also to state which itself is modified in the function body.
Alternatively, I can use watch(pageUrl, async pageUrl => { ... }), but this seems only to be triggered when pageUrl changes (in my case: I modify the URL because the props are updated via vue-router, but not when I initially visit the URL).
What should I do here, is my idea of signalling the loading state not appropriate here?
From a logical point of view, the page is a computed value, the only reason I use watch here is that it's asynchronous and might yield an error as well.
Thanks to Husam I got aware of the bug, and it seems like changing a piece of state twice introduces this behaviour - in my case setting loading to true and then again to false.
This behaviour is not apparent in Vue3, and a workaround (and in general maybe the much cleaner method) could be to directly use watch instead of watchEffect.
The source code shows different overloads of the funciton, and there is an options argument that is not directly documented in the Vue3 API. There, I found that my call above needs to read like watch(value, async value => { effect }, { immediate: true }).
I need to perform a certain action whenever a call to router.push is triggered.
I'm trying to use Vue-Router's navigation guards for this, but there is no way to tell, inside of its callback, what method (go/push/back/replace) triggered it.
router.beforeResolve((to, from) => {
// Do something only if this was triggered by "push"
});
Just hook vue-router push/back/replace function before Vue.use(vue-router),
then get navigation type by call
this.$router.customNaviType;
import Vue from 'vue'
import Router from 'vue-router'
const routerPush = Router.prototype.push;
// rewrite push
Router.prototype.push = function push(location) {
this.customNaviType = "push";
return routerPush.call(this, location).catch(error => error)
}
const routerBack = Router.prototype.back;
// rewrite back
Router.prototype.back = function back() {
this.customNaviType = "back";
return routerBack.call(this);
}
const routerReplace = Router.prototype.replace;
// rewrite replace
Router.prototype.replace = function replace(location) {
this.customNaviType = "replace";
return routerReplace.call(this, location).catch(error => error)
}
Vue.use(Router)
https://router.vuejs.org/guide/essentials/navigation.html
By my understanding, only push method will increase the history.length by one.
Maybe use a global variable to keep check window.history.length. If it increase, then you can trigger your push event.
For example:
router.beforeResolve((to, from) => {
if (window.history.length > window.last_history_length) {
trigger_your_push_event();
}
window.last_history_length = window.history.length;
}
});
It can not be catched by navigation guards directly:
But,
using the state of your app you can have a better idea which operation is done. You can do it by saving the current and your last route to your state using the guard afterEach. Once you know them, you can compare them with from and to parameters in e.g. beforeEach to get know whether it is a push or back. You can probably add more metadata to your routes so you get know more about your routes to decide whether it is replaced by some kind of other type route:
I've searched a lot, but there is no clear answer to that. Basically, what should be the best practice to automatically change a route after a mutation?
Ex: I click a button to login() -> action login that makes an http call -> mutation LOGIN_SUCCESSFUL -> I want to redirect the user to the main page $router.go()
Should I wrap the action in a Promise, and then listen to the result to call the route change from the component?
Should I do it directly from the $store?
Does vuex-router-sync helps in any way?
Thanks a lot!
The answer to this questions seems to be somewhat unclear in the Vue community.
Most people (including me) would say that the store mutation should not have any effects besides actually mutating the store. Hence, doing the route change directly in the $store should be avoided.
I have very much enjoyed going with your first suggestion: Wrapping the action in a promise, and changing the route from withing your component as soon as the promise resolves.
A third solution is to use watch in your component, in order to change the route as soon as your LOGGED_IN_USER state (or whatever you call it) has changed. While this approach allows you to keep your actions and mutations 100% clean, I found it to become messy very, very quickly.
As a result, I would suggest going the promise route.
Put an event listener on your app.vue file then emit en event by your mutation function. But I suggest you wrapping the action in a promise is good way
App.vue:
import EventBus from './eventBus';
methods: {
redirectURL(path) {
this.$router.go(path)}
},
created() {
EventBus.$on('redirect', this.redirectURL)
}
mutation:
import EventBus from './eventBus';
LOGIN_SUCCESSFUL() {
state.blabla = "blabla";
EventBus.$emit('redirect', '/dashboard')
}
As of now (mid 2018) API of Vuex supports subscriptions. Using them it is possible to be notified when a mutation is changing your store and to adjust the router on demand.
The following example is an excerpt placed in created() life-cycle hook of a Vue component. It is subscribing to mutations of store waiting for the first match of desired criteria to cancel subscriptions and adjust route.
{
...
created: function() {
const unsubscribe = this.$store.subscribe( ( mutation, state ) => {
if ( mutation.type === "name-of-your-mutation" && state.yourInfo === desiredValue ) {
unsubscribe();
this.$router.push( { name: "name-of-your-new-route" } );
}
} );
},
...
}
The nice thing about beforeRouteLeave is that you can prevent navigating away under certain conditions.
I have a setup that uses a subroute to render part of the page. I would like a navigation guard on the subroute to prevent switching to another one if the data is not saved.
{
path: '/customers/view',
component: ViewCustomerShell,
children: [
{path: ':id', name: 'ViewCustomer', component: ViewCustomer}
]
},
So when I visit /customers/view/12 and make a change, if they try to load /customers/view/13, I want to pop up the usual confirmation and potentially stop navigation. Since beforeRouteLeave is not called in this situation, what is the recommended approach for preventing navigation? It seems that watching $route would be too late, because then the navigation has already occurred.
Note: As mentioned above, beforeRouteLeave is not called in this situation; it doesn't work.
Note: Using onbeforeunload doesn't work because it only triggers when the entire page changes.
I have also posted the same answer here.
Dynamic route matching is specifically designed to make different paths or URLs map to the same route or component. Therefor, changing the argument does not technically count as leaving (or changing) the route, therefor beforeRouteLeave rightly does not get fired.
However, I suggest that one can make the component corresponding to the route responsible for detecting changes in the argument. Basically, whenever the argument changes, record the change then reverse it (hopefully reversal will be fast enough that it gets unnoticed by the user), then ask for confirmation. If user confirms the change, then use your record to "unreverse" the change, but if the user does not confirm, then keep things as they are (do not reverse the reverse).
I have not tested this personally and therefor I do not gurantee it to work, but hopefully it would have cleared up any confusion as to which part of the app is responsible for checking what change.
I know that this post is very old. but it was the first one I found when looking for the same problem.
I have no idea if there is a better solution nowadays but for those who are looking for a solution, I can share mine:
1. Define a global state
let isRouteChangeBlocked: boolean = false;
export function blockRouteChange(set?: boolean): boolean {
if (arguments.length == 1) {
isRouteChangeBlocked = !!set;
return isRouteChangeBlocked;
}
return isRouteChangeBlocked;
}
2. Replace the route function
const originalPush = VueRouter.prototype.push;
VueRouter.prototype.push = function(location: RawLocation) {
if (blockRouteChange()) {
if (confirm("Du hast ungespeicherte Änderungen, möchtest du fortfahren?")) {
blockRouteChange(false);
return originalPush.call(this, location) as any;
}
return;
}
return originalPush.call(this, location) as any;
};
3. Set the state
#Watch("note.text")
private noteTextChanged() {
blockRouteChange(true);
}
This does exactly what I want. If nowadays there is a better solution, let me know. You can get the full runnable example here: https://github.com/gabbersepp/dev.to-posts/tree/master/blog-posts/vuejs-avoid-routes/code/example
You could use a $route object inside your component to watch if it changes and then raise up the confirmation modal... This will get called whenever your route changes!
const Baz = {
data () {
return { saved: false }
},
template: `
<div>
<p>baz ({{ saved ? 'saved' : 'not saved' }})<p>
<button #click="saved = true">save</button>
</div>
`,
watch: {
'$route': function () {
if (this.saved || window.confirm('Not saved, are you sure you want to navigate away?')) {
// do something ...
}
}
}