I'm trying to create pagination for my site on Vue.js.
I have two buttons:
<button #click.prevent="onPrevBtnClick">previous</button>
<button #click.prevent="onNextBtnClick">next</button>
Which pass to my main component:
methods: {
onPrevBtnClick () {
this.$emit('prev-button')
},
onNextBtnClick () {
this.$emit('next-button')
}
}
Basically, I want to make a query according to currentPage
async fetchMovies () {
try {
const fetchData = await axios.get(`${process.env.VUE_APP_API_URL}/discover/movie&api_key=${process.env.VUE_APP_API_KEY}&page=${this.currentPage}`)
this.movies = {...fetchData.data.results}
}
catch (e) {
console.log(e)
}
},
async onPrevBtnClick () {
this.currentPage--
},
async onNextBtnClick () {
this.currentPage++
}
I try to change them through a method, also tried through the computed but for some reason will not change dynamically.
I will be grateful for your help.
If you want this.movies to be updated when the user clicks "previous" or "next" you'll have to call the fetchMovies method in the onPrevBtnClick and onNextBtnClick methods. Currently onPrevBtnClick and onNextBtnClick only update this.currentPage, but doing so will not automatically cause fetchMovies to execute if fetchMovies is a method.
An alternative approach would be to make this.movies a computed property that is based on this.currentPage and get rid of fetchMovies, putting that logic in the computed property.
Check out the guide on Computed Properties and Watchers for more information. The key things to understand are:
"computed properties are cached based on their reactive dependencies. A computed property will only re-evaluate when some of its reactive dependencies have changed."
Methods never reevaluate on their own like computed properties. Methods need you to explicitly call them.
I am using Nuxt js SSR for an app that am build, I installed Vue Event plugin but when i emit an event it runs twice at the listener. Created hook runs twice too.
Modules am using:
Axios, Auth, Toast
Child Component
methods: {
initPlaylist(songs) {
console.log(songs)
}
},
mounted () {
this.$events.$on('playAll', data => {
this.initPlaylist(data.songs) //runs twice
})
}
Parent Component
method () {
playAll (songs) {
this.$events.$emit('playAll', songs)
}
}
How can i resolve this issues guys? I need your help.
Maybe you have to call that parent's method on client side only.
you can write code like this to prevent emit on server side:
methods: {
playAll(songs) {
if (process.server) return
this.$events.$emit('playAll', songs)
}
}
or do not call playAll method on server side. (eg: created, mounted...)
You need to off that event first before.
this.$events.$off("playAll");
this.$events.$on('playAll', data => {
this.initPlaylist(data.songs) //runs twice
})
I need some help in vuejs 2. I want to detect back button pressed event. I did some research and found this,
document.addEventListener("backbutton", yourCallBackFunction, false");
I think it is global event. I need something local, within a method. where i can use some logic.
methods: {
backButtonPressed() {
}
}
Or can i bind the global one to local function? Can anyone help me with that? TIA
Add the event on your mounted method on your root Vue component (the one the Vue instance is tied to.
var app = new Vue({
el: '#app',
data: {
message: 'Hello Vue!'
},
methods: {
yourCallBackFunction () {
// Your logic
}
}
mounted () {
document.addEventListener("backbutton", this.yourCallBackFunction, false);
},
beforeDestroy () {
document.removeEventListener("backbutton", this.yourCallBackFunction);
}
})
We also remove it on beforeDestroy to keep things tidy.
Note: I've not personally used the back button event so have added it to this example only because you say it's working but need a way to globally handle it. This code will do just that.
Note: As per #Luke's comment - we add the listener in the mounted event so it doesn't execute for in the SSR context. If SSR isn't a factor / consideration then we can use the created lifecycle hook.
If still someone come across this issue.
A solution for an event listener for browser-back is https://developer.mozilla.org/de/docs/Web/API/WindowEventHandlers/onpopstate
window.onpopstate = function() {
alert('browser-back');
};
Is easy, if you need to catch that behavior only your component, you can use beforeRouteLeave function in the root of your component.
Example:
beforeRouteLeave (to, from, next) {
const answer = window.confirm('Do you really want to leave?)
if (answer) {
next()
} else {
next(false)
}
}
But if you need to add this behavior globally, you need catch with beforeEnter in the routes.
If you are using vue-router(no idea if you don't, why...) a good solution is to use in your component:
beforeRouteLeave(to, from, next) {
if (from.name === 'nameOfFromRoute' && to.name === 'nameOfToRoute' ) {
next(false);
} else {
next();
}
console.log({ to, from });
},
This was one variation I found to work as well, a little less verbose and uses router.push in the beforeDestroy lifecycle method
Listen for popstate
Push the desired name/path to redirect
The code below would be a better understanding.
beforeDestroy() {
window.addEventListener("popstate", (event) => {
this.$router.push({ path: <your path> });
});
},
This implementation was on Nuxt 2.14.6 and works just as well with all versions of Vue.
I have a similar problem and solved using #click="backFunction"
and created the function on methods like this:
methods: {
backFunction(){
//yourlogic
},
I have a login modal that I activate by setting .is-active to it. For this, I have a method like this:
methods: {
toggleModal: function (event) {
this.isActive = !this.isActive
}
}
that I run onclick. Depending on the boolean value of isActive, my modal gets the class .is-active.
Thing is, in my modal I have a button that takes the user to a new view which means it's rendering a new component, with this code:
<router-link class="control" #click="toggleModal()" to="/register">
As you can see, it's routing to /register. Before doing this, I need to run toggleModal() so that the modal gets closed. Right now it's routing without running the method which means that the new view has my modal overlay which is... not optimal.
Is there any good way to do this in Vue? Could I maybe create a method, that first calls toggleModal(), and then routes from the method?
Thanks.
I would define a method that calls toggleModal first, then navigates. Like so:
methods: {
navigateAway () {
this.isActive = !this.isActive
this.$router.push('/register')
}
}
You don't need the event argument unless you intend on capturing more data from the event or event target. You could also wrap the router push in a setTimeout if you so desire, for perhaps cleaner looking view changes.
methods: {
navigateAway () {
let vm = this
vm.isActive = !vm.isActive
setTimeout(function () {
vm.$router.push('/register')
}, 50)
}
}
Of course, there are hooks that you can use from vue-router that make this easy. Example (assuming you're using single file components and Vue.js 2.x):
export default {
data () {
return {
isActive: false
}
},
beforeRouteLeave (to, from, next) {
this.isActive = false // I assume that you would not want to leave it open upon navigating away
next()
}
}
Link to vue router hooks: https://router.vuejs.org/en/advanced/navigation-guards.html
It seems that Vue.js 2.0 doesn't emit events from a grand child to his grand parent component.
Vue.component('parent', {
template: '<div>I am the parent - {{ action }} <child #eventtriggered="performAction"></child></div>',
data(){
return {
action: 'No action'
}
},
methods: {
performAction() { this.action = 'actionDone' }
}
})
Vue.component('child', {
template: '<div>I am the child <grand-child></grand-child></div>'
})
Vue.component('grand-child', {
template: '<div>I am the grand-child <button #click="doEvent">Do Event</button></div>',
methods: {
doEvent() { this.$emit('eventtriggered') }
}
})
new Vue({
el: '#app'
})
This JsFiddle solves the issue https://jsfiddle.net/y5dvkqbd/4/ , but by emtting two events:
One from grand child to middle component
Then emitting again from middle component to grand parent
Adding this middle event seems repetitive and unneccessary. Is there a way to emit directly to grand parent that I am not aware of?
Vue 2.4 introduced a way to easily pass events up the hierarchy using vm.$listeners
From https://v2.vuejs.org/v2/api/#vm-listeners :
Contains parent-scope v-on event listeners (without .native modifiers). This can be passed down to an inner component via v-on="$listeners" - useful when creating transparent wrapper components.
See the snippet below using v-on="$listeners" in the grand-child component in the child template:
Vue.component('parent', {
template:
'<div>' +
'<p>I am the parent. The value is {{displayValue}}.</p>' +
'<child #toggle-value="toggleValue"></child>' +
'</div>',
data() {
return {
value: false
}
},
methods: {
toggleValue() { this.value = !this.value }
},
computed: {
displayValue() {
return (this.value ? "ON" : "OFF")
}
}
})
Vue.component('child', {
template:
'<div class="child">' +
'<p>I am the child. I\'m just a wrapper providing some UI.</p>' +
'<grand-child v-on="$listeners"></grand-child>' +
'</div>'
})
Vue.component('grand-child', {
template:
'<div class="child">' +
'<p>I am the grand-child: ' +
'<button #click="emitToggleEvent">Toggle the value</button>' +
'</p>' +
'</div>',
methods: {
emitToggleEvent() { this.$emit('toggle-value') }
}
})
new Vue({
el: '#app'
})
.child {
padding: 10px;
border: 1px solid #ddd;
background: #f0f0f0
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>
<div id="app">
<parent></parent>
</div>
NEW ANSWER (Nov-2018 update)
I discovered that we could actually do this by leveraging the $parent property in the grand child component:
this.$parent.$emit("submit", {somekey: somevalue})
Much cleaner and simpler.
The Vue community generally favors using Vuex to solve this kind of issue. Changes are made to Vuex state and the DOM representation just flows from that, eliminating the need for events in many cases.
Barring that, re-emitting would probably be the next best choice, and lastly you might choose to use an event bus as detailed in the other highly voted answer to this question.
The answer below is my original answer to this question and is not an approach I would take now, having more experience with Vue.
This is a case where I might disagree with Vue's design choice and resort to DOM.
In grand-child,
methods: {
doEvent() {
try {
this.$el.dispatchEvent(new Event("eventtriggered"));
} catch (e) {
// handle IE not supporting Event constructor
var evt = document.createEvent("Event");
evt.initEvent("eventtriggered", true, false);
this.$el.dispatchEvent(evt);
}
}
}
and in parent,
mounted(){
this.$el.addEventListener("eventtriggered", () => this.performAction())
}
Otherwise, yes, you have to re-emit, or use a bus.
Note: I added code in the doEvent method to handle IE; that code could be extracted in a reusable way.
Yes, you're correct events only go from child to parent. They don't go further, e.g. from child to grandparent.
The Vue documentation (briefly) addresses this situation in the Non Parent-Child Communication section.
The general idea is that in the grandparent component you create an empty Vue component that is passed from grandparent down to the children and grandchildren via props. The grandparent then listens for events and grandchildren emit events on that "event bus".
Some applications use a global event bus instead of a per-component event bus. Using a global event bus means you will need to have unique event names or namespacing so events don't clash between different components.
Here is an example of how to implement a simple global event bus.
If you want to be flexible and simply broadcast an event to all parents and their parents recursively up to the root, you could do something like:
let vm = this.$parent
while(vm) {
vm.$emit('submit')
vm = vm.$parent
}
Another solution will be on/emit at root node:
Uses vm.$root.$emit in grand-child, then uses vm.$root.$on at the ancestor (or anywhere you'd like).
Updated: sometimes you'd like to disable the listener at some specific situations, use vm.$off (for example: vm.$root.off('event-name') inside lifecycle hook=beforeDestroy).
Vue.component('parent', {
template: '<div><button #click="toggleEventListener()">Listener is {{eventEnable ? "On" : "Off"}}</button>I am the parent - {{ action }} <child #eventtriggered="performAction"></child></div>',
data(){
return {
action: 1,
eventEnable: false
}
},
created: function () {
this.addEventListener()
},
beforeDestroy: function () {
this.removeEventListener()
},
methods: {
performAction() { this.action += 1 },
toggleEventListener: function () {
if (this.eventEnable) {
this.removeEventListener()
} else {
this.addEventListener()
}
},
addEventListener: function () {
this.$root.$on('eventtriggered1', () => {
this.performAction()
})
this.eventEnable = true
},
removeEventListener: function () {
this.$root.$off('eventtriggered1')
this.eventEnable = false
}
}
})
Vue.component('child', {
template: '<div>I am the child <grand-child #eventtriggered="doEvent"></grand-child></div>',
methods: {
doEvent() {
//this.$emit('eventtriggered')
}
}
})
Vue.component('grand-child', {
template: '<div>I am the grand-child <button #click="doEvent">Emit Event</button></div>',
methods: {
doEvent() { this.$root.$emit('eventtriggered1') }
}
})
new Vue({
el: '#app'
})
<script src="https://unpkg.com/vue/dist/vue.js"></script>
<div id="app">
<parent></parent>
</div>
VueJS 2 components have a $parent property that contains their parent component.
That parent component also includes its own $parent property.
Then, accessing the "grandparent" component it's a matter of accessing the "parent's parent" component:
this.$parent["$parent"].$emit("myevent", { data: 123 });
Anyway, this is kinda tricky, and I recommend using a global state manager like Vuex or similar tools, as other responders have said.
I've made a short mixin based on #digout answer. You want to put it, before your Vue instance initialization (new Vue...) to use it globally in project. You can use it similarly to normal event.
Vue.mixin({
methods: {
$propagatedEmit: function (event, payload) {
let vm = this.$parent;
while (vm) {
vm.$emit(event, payload);
vm = vm.$parent;
}
}
}
})
Riffing off #kubaklam and #digout's answers, this is what I use to avoid emitting on every parent component between the grand-child and the (possibly distant) grandparent:
{
methods: {
tunnelEmit (event, ...payload) {
let vm = this
while (vm && !vm.$listeners[event]) {
vm = vm.$parent
}
if (!vm) return console.error(`no target listener for event "${event}"`)
vm.$emit(event, ...payload)
}
}
}
When building out a component with distant grand children where you don't want many/any components to be tied to the store, yet want the root component to act as a store/source of truth, this works quite well. This is similar to the data down actions up philosophy of Ember. Downside is that if you want to listen for that event on every parent in between, then this won't work. But then you can use $propogateEmit as in above answer by #kubaklam.
Edit: initial vm should be set to the component, and not the component's parent. I.e. let vm = this and not let vm = this.$parent
This is the only case when I use event bus!! For passing data from deep nested child, to not directly parent, communication.
First: Create a js file (I name it eventbus.js) with this content:
import Vue from 'vue'
Vue.prototype.$event = new Vue()
Second: In your child component emit an event:
this.$event.$emit('event_name', 'data to pass')
Third: In the parent listen to that event:
this.$event.$on('event_name', (data) => {
console.log(data)
})
Note: If you don't want that event anymore please unregister it:
this.$event.$off('event_name')
INFO: No need to read the below personal opinion
I don't like to use vuex for grand-child to grand-parent communication (Or similar communication level).
In vue.js for passing data from grand-parent to grand-child you can use provide/inject. But there is not something similar for the opposite thing. (grand-child to grand-parent) So I use event bus whenever I have to do that kind of communication.
Riffing off #digout answer. I am thinking that if the purpose is to send data to a far-ancestor then we don't need $emit at all. I did this for my edge-case and it seems to work. Yes, it could be implemented via a mixin but it doesn't have to be.
/**
* Send some content as a "message" to a named ancestor of the component calling this method.
* This is an edge-case method where you need to send a message many levels above the calling component.
* Your target component must have a receiveFromDescendant(content) method and it decides what
* to do with the content it gets.
* #param {string} name - the name of the Vue component eg name: 'myComponentName'
* #param {object} content - the message content
*/
messageNamedAncestor: function (name, content) {
let vm = this.$parent
let found = false
while (vm && !found) {
if (vm.$vnode.tag.indexOf('-' + name) > -1) {
if (vm.receiveFromDescendant) {
found = true
vm.receiveFromDescendant(content)
} else {
throw new Error(`Found the target component named ${name} but you dont have a receiveFromDescendant method there.`)
}
} else {
vm = vm.$parent
}
}
}
Given an ancestor:
export default {
name: 'myGreatAncestor',
...
methods: {
receiveFromDescendant (content) {
console.log(content)
}
}
}
A great grand-child says
// Tell the ancestor component something important
this.messageNamedAncestor('myGreatAncestor', {
importantInformation: 'Hello from your great descendant'
})
As of Vue 3, a number of fundamental changes have happened to root events:
The $on, $off and $once root methods no longer exist. There is to a certain extent something to replace this, since you can listen to root events by doing this:
createApp(App, {
// Listen for the 'expand' event
onExpand() {
console.log('expand')
}
})
Another solution are event buses, but the Vue.js documents take a dim view - they can cause maintenance headaches in the long run. You might get an ever spreading set of emits and event sinks, with no clear or central idea of how it is managed or what components could be affected elsewhere. Nonetheless, examples given by the docs of event buses are mitt and tiny-emitter.
However the docs make it clear that they recommend handling these sorts of situations in this order:
Props A convenient solution for parent / child communications.
Provide/Inject A simple way for ancestors to communicate with their descendants (although critically, not the other way around).
Vuex A way of handling global state in a clear fashion. It's important to note that this is not solely for events, or communications - Vuex was built primarily to handle state.
Essentially the choice for the OP would come down to using an event bus, or Vuex. In order to centralise the event bus, you could place it inside Vuex, if state was also needed to be globally available. Otherwise using an event bus with strict centralised controls on it's behaviour and location might help.
I really dig the way this is handled by creating a class that is bound to the window and simplifying the broadcast/listen setup to work wherever you are in the Vue app.
window.Event = new class {
constructor() {
this.vue = new Vue();
}
fire(event, data = null) {
this.vue.$emit(event, data);
}
listen() {
this.vue.$on(event, callback);
}
}
Now you can just fire / broadcast / whatever from anywhere by calling:
Event.fire('do-the-thing');
...and you can listen in a parent, grandparent, whatever you want by calling:
Event.listen('do-the-thing', () => {
alert('Doing the thing!');
});