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Vuejs - keep-alive component toggled with v-if

###The Problem
I have a child component that may or may not exist on the page with a v-if. Trying to keep it cached when the user has clicked other things so that search terms and whatnot show up again when the user returns fails no matter how I try to cache with <keep-alive>.
###What I've tried
The documentation seems to indicate that all I need to do is wrap my component in a <keep-alive> tag and things should just work. I tried matching some documentation that uses the <component> tag which clearly doesn't work. I also tried using the include prop since just wrapping it doesn't work.
Vue.component('child', {
template: '<div>child: {{text}}<div>',
data() {return {text: ""}},
created(){
this.$nextTick(() => {
this.text = `${Math.round(Math.random() * 100)}`
})
},
activated: function() {
this.$nextTick(() => {
console.log('in activated');
});
}
})
var vm = new Vue({
el: '#app',
data: function() {
return {
showNow:false,
message: 'This is a test.'
}
},
methods: {
changeText: function() {
this.message = 'changed';
},
toggle() {
this.showNow = !this.showNow
}
},
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.4.2/vue.min.js"></script>
<div id="app">
<keep-alive include="child">
<div v-if="showNow">
<h4>Title of section to be toggled</h4>
<component is="child"></component>
</div>
</keep-alive>
<button #click="toggle()">toggle child</button>
</div>
I've also tried not using include and just wrapping like so <keep-alive><child></child></keep-alive> or using the <component> syntax and neither of those work either.
If you remove the conditional rendering, the activated hook is called, but that obviously defeats the purpose of <keep-alive>! As it stands right now, that hook is never called, which is frustrating.
Also, the example in the documentation doesn't help either because they're not using v-if, just changing which components are rendered via a string....
P.S. I have no idea how to tag this other than Vue.js

Here is a lightly modified version of your code with keep-alive working correctly:
Vue.component('child', {
template: '<div>child: {{text}}</div>',
data() {return {text: ""}},
created(){
console.log('in created')
this.$nextTick(() => {
this.text = `${Math.round(Math.random() * 100)}`
})
},
activated: function() {
this.$nextTick(() => {
console.log('in activated');
});
}
})
var vm = new Vue({
el: '#app',
data: function() {
return {
showNow:false,
message: 'This is a test.'
}
},
methods: {
changeText: function() {
this.message = 'changed';
},
toggle() {
this.showNow = !this.showNow
}
},
});
<script src="https://unpkg.com/vue#2.6.11/dist/vue.js"></script>
<div id="app">
<keep-alive>
<child v-if="showNow"></child>
</keep-alive>
<button #click="toggle()">toggle child</button>
</div>
The created hook is only called the first time. On subsequent activation the activated hook is called but not created.
The key change is that the <child> component must be a direct child of <keep-alive>. This direct child must also be the component that has the v-if.
You can't use a <div> for this purpose as <keep-alive> specifically looks for a component, not just an element. See:
https://github.com/vuejs/vue/blob/ec78fc8b6d03e59da669be1adf4b4b5abf670a34/src/core/components/keep-alive.js#L85
Another common mistake with keep-alive is to put a v-if on the keep-alive component itself, or on one of its ancestors. This won't work as the keep-alive component itself will be destroyed. The keep-alive component maintains a cache of child components but if the keep-alive is itself destroyed then that cache is lost.

How to create Vue.js slot programmatically?

I have the following component with a slot:
<template>
<div>
<h2>{{ someProp }}</h2>
<slot></slot>
</div>
</template>
For some reasons, I have to manually instantiate this component. This is how I am doing it:
const Constr = Vue.extend(MyComponent);
const instance = new Constr({
propsData: { someProp: 'My Heading' }
}).$mount(body);
The problem is: I am not able to create slot contents programmatically. So far, I can create simple string based slot:
const Constr = Vue.extend(MyComponent);
const instance = new Constr({
propsData: { someProp: 'My Heading' }
});
// Creating simple slot
instance.$slots.default = ['Hello'];
instance.$mount(body);
The question is - how can I create $slots programmatically and pass it to the instance I am creating using new?
Note: I am not using a full build of Vue.js (runtime only). So I don't have a Vue.js compiler available to compile the template on the fly.

I looked into TypeScript definition files of Vue.js and I found an undocumented function on Vue component instance: $createElement(). My guess is, it is the same function that is passed to render(createElement) function of the component. So, I am able to solve it as:
const Constr = Vue.extend(MyComponent);
const instance = new Constr({
propsData: { someProp: 'My Heading' }
});
// Creating simple slot
const node = instance.$createElement('div', ['Hello']);
instance.$slots.default = [node];
instance.$mount(body);
But this is clearly undocumented and hence questionable approach. I will not mark it answered if there is some better approach available.

I think I have finally stumbled on a way to programmatically create a slot element. From what I can tell, the approach does not seem to work for functional components. I am not sure why.
If you are implementing your own render method for a component, you can programmatically create slots that you pass to child elements using the createElement method (or whatever you have aliased it to in the render method), and passing a data hash that includes { slot: NAME_OF_YOUR_SLOT } followed by the array of children within that slot.
For example:
Vue.config.productionTip = false
Vue.config.devtools = false;
Vue.component('parent', {
render (createElement) {
return createElement('child', [
createElement('h1', { slot: 'parent-slot' }, 'Parent-provided Named Slot'),
createElement('h2', { slot: 'default' }, 'Parent-provided Default Slot')
])
}
})
Vue.component('child', {
template: '<div><slot name="parent-slot" /><slot /></div>'
})
new Vue({
el: '#app',
template: '<parent />'
})
<script src="https://cdn.jsdelivr.net/npm/vue#2.5.17/dist/vue.js"></script>
<div id='app'>
</div>

(This doesn't really answer How to create Vue.js slot programatically?. But it does solve your problem.)
This trick is less hackish compared to using $createElement().
Basically, create a new component that register MyComponent as a local component.
const Constr = Vue.extend({
template: `
<MyComponent someProp="My Heading">
<div>slot here !!!</div>
</MyComponent>
`,
components: {
MyComponent: MyComponent
}
});
const instance = new Constr().$mount('#app');
Demo: https://jsfiddle.net/jacobgoh101/shrn26p1/

I just came across an answer to this in vue forum:
slots
The principle is: There is nothing like createElement('slot'..)
Instead there is a render function which provides the slotted innerHtml as function:
$scopedSlots.default()
Usage:
render: function (createElement) {
const self = this;
return createElement("div", this.$scopedSlots.default());
}
If you want to provide a default in case there is no content given for the slots, you need to code a disctinction yourself and render something else.
(The link above holds a more detailed example)
The function returns an array, therefore it can not be used as a root for the render function. It need to be wrapped into single container node like div in the example above.

Vuex how to Access state data on component mounted or created hook?

I'm trying to create a Quill.js editor instance once component is loaded using mounted() hook. However, I need to set the Quill's content using Quill.setContents() on the same mounted() hook with the data I received from vuex.store.state .
My trouble here is that the component returns empty value for the state data whenever I try to access it, irrespective of being on mounted() or created() hooks. I have tried with getters and computed properties too. Nothing seems to work.
I have included my entry.js file, concatenated all the components to make things simpler for you to help me.
Vue.component('test', {
template:
`
<div>
<ul>
<li v-for="note in this.$store.state.notes">
{{ note.title }}
</li>
</ul>
{{ localnote }}
<div id="testDiv"></div>
</div>
`,
props: ['localnote'],
data() {
return {
localScopeNote: this.localnote,
}
},
created() {
this.$store.dispatch('fetchNotes')
},
mounted() {
// Dispatch action from store
var quill = new Quill('#testDiv', {
theme: 'snow'
});
// quill.setContents(JSON.parse(this.localnote.body));
},
methods: {
setLocalCurrentNote(note) {
console.log(note.title)
return this.note = note;
}
}
});
const store = new Vuex.Store({
state: {
message: "",
notes: [],
currentNote: {}
},
mutations: {
setNotes(state,data) {
state.notes = data;
// state.currentNote = state.notes[1];
},
setCurrentNote(state,note) {
state.currentNote = note;
}
},
actions: {
fetchNotes(context) {
axios.get('http://localhost/centaur/public/api/notes?notebook_id=1')
.then( function(res) {
context.commit('setNotes', res.data);
context.commit('setCurrentNote', res.data[0]);
});
}
},
getters: {
getCurrentNote(state) {
return state.currentNote;
}
}
});
const app = new Vue({
store
}).$mount('#app');
And here is the index.html file where I'm rendering the component:
<div id="app">
<h1>Test</h1>
<test :localnote="$store.state.currentNote"></test>
</div>
Btw, I have tried the props option as last resort. However, it didn't help me in anyway. Sorry if this question is too long. Thank you for taking your time to read this. Have a nice day ;)

I copied your code and tested it ( of-course I created my own dummy notes so I could remove the get request ) and I was able to get the notes display on a page.
A couple of things that I realized from your code, you may need to add a store property as there are places in your component ( test ) where you are referencing it, yet you only define it on the 'app' component. So in this section of your code modify as shown below:
props: ['localnote'],
data() {
return {
localScopeNote: this.localnote,
store : store
}
},
The key difference is the definition of the 'store' property. Please note that, what you have done, defining a "store" property in your app component, is correct, but the very same needs to be defined in "test" component as I have shown in the above code snippet above.
Second thing is, you are using $store and I guess that gives you undefined, unless as you said, in the libraries that you included this resolves accordingly, but on my side I had to remove all references of "$store" and replace it with just "store" (without the dollar sign).
Lastly for testing purposes, I would advise you to also

How to access a component property from App.vue

I used vue-loader to help me install vue and webpack
I have a file called App.vue
In App.vue I added a component called widget. If I clicked some button there's a function that set the btnClicked = true hence the widget appears
<widget v-show="btnClicked"></widget>
but I also want that function to access the widgetShowMe, it's a property in my component.
I want the function activated in my App.vue to also set widgetShowMe = true
I tried this but it didn't work
methods:{
btnClickedFunc () {
this.btnClicked = true;
Widget.widgetShowMe = true;
}
}

Accessing child component's data in parent component in vuejs
If you have a parent component called parent and child component called child, you can communicate between each other using props and events.
props: Facilitates communication from parent to child.
events: Can be used to pass data in a child component to the parent component.
For this question we require events and will use v-model to make the child component usable everywhere with much less setup.
Vue.component('counter', {
template: `<div><button #click='add'>+1</button>
<button #click='sub'>-1</button>
<div>this is inside the child component: {{ result }}</div></div>`,
data () {
return {
result: 0
}
},
props: ['value'],
methods: {
emitResult () {
this.$emit('input', this.result)
},
add () {
this.result += 1
this.emitResult()
},
sub () {
this.result -= 1
this.emitResult()
}
}
})
new Vue({
el: '#demo',
data () {
return {
resultFromChild: null
}
}
})
<script src="https://vuejs.org/js/vue.min.js"></script>
<div id='demo'>
<counter v-model='resultFromChild'></counter>
This is in parent component {{ resultFromChild }}
</div>
Custom component with v-model
This needs two requirements.
You have a prop on the child component with the name value.
props: ['value'], // this part in the child component snippet
You emit the event input with the value.
this.$emit('input', this.result) // this part in the child component snippet
All you need to think of is, when to emit the event with the value of widgetShowMe, and your app.vue can easily capture the value inside your widget.

Call a Vue.js component method from outside the component

Let's say I have a main Vue instance that has child components. Is there a way of calling a method belonging to one of these components from outside the Vue instance entirely?
Here is an example:
var vm = new Vue({
el: '#app',
components: {
'my-component': {
template: '#my-template',
data: function() {
return {
count: 1,
};
},
methods: {
increaseCount: function() {
this.count++;
}
}
},
}
});
$('#external-button').click(function()
{
vm['my-component'].increaseCount(); // This doesn't work
});
<script src="http://vuejs.org/js/vue.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="app">
<my-component></my-component>
<br>
<button id="external-button">External Button</button>
</div>
<template id="my-template">
<div style="border: 1px solid; padding: 5px;">
<p>A counter: {{ count }}</p>
<button #click="increaseCount">Internal Button</button>
</div>
</template>
So when I click the internal button, the increaseCount() method is bound to its click event so it gets called. There is no way to bind the event to the external button, whose click event I am listening for with jQuery, so I'll need some other way to call increaseCount.
EDIT
It seems this works:
vm.$children[0].increaseCount();
However, this is not a good solution because I am referencing the component by its index in the children array, and with many components this is unlikely to stay constant and the code is less readable.

In the end I opted for using Vue's ref directive. This allows a component to be referenced from the parent for direct access.
E.g.
Have a component registered on my parent instance:
var vm = new Vue({
el: '#app',
components: { 'my-component': myComponent }
});
Render the component in template/html with a reference:
<my-component ref="foo"></my-component>
Now, elsewhere I can access the component externally
<script>
vm.$refs.foo.doSomething(); //assuming my component has a doSomething() method
</script>
See this fiddle for an example: https://jsfiddle.net/0zefx8o6/
(old example using Vue 1: https://jsfiddle.net/6v7y6msr/)
Edit for Vue3 - Composition API
The child-component has to return the function in setup you want to use in the parent-component otherwise the function is not available to the parent.
Note: <sript setup> doc is not affacted, because it provides all the functions and variables to the template by default.

You can set ref for child components then in parent can call via $refs:
Add ref to child component:
<my-component ref="childref"></my-component>
Add click event to parent:
<button id="external-button" #click="$refs.childref.increaseCount()">External Button</button>
var vm = new Vue({
el: '#app',
components: {
'my-component': {
template: '#my-template',
data: function() {
return {
count: 1,
};
},
methods: {
increaseCount: function() {
this.count++;
}
}
},
}
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>
<div id="app">
<my-component ref="childref"></my-component>
<button id="external-button" #click="$refs.childref.increaseCount()">External Button</button>
</div>
<template id="my-template">
<div style="border: 1px solid; padding: 2px;" ref="childref">
<p>A counter: {{ count }}</p>
<button #click="increaseCount">Internal Button</button>
</div>
</template>

For Vue2 this applies:
var bus = new Vue()
// in component A's method
bus.$emit('id-selected', 1)
// in component B's created hook
bus.$on('id-selected', function (id) {
// ...
})
See here for the Vue docs.
And here is more detail on how to set up this event bus exactly.
If you'd like more info on when to use properties, events and/ or centralized state management see this article.
See below comment of Thomas regarding Vue 3.

You can use Vue event system
vm.$broadcast('event-name', args)
and
vm.$on('event-name', function())
Here is the fiddle:
http://jsfiddle.net/hfalucas/wc1gg5v4/59/

A slightly different (simpler) version of the accepted answer:
Have a component registered on the parent instance:
export default {
components: { 'my-component': myComponent }
}
Render the component in template/html with a reference:
<my-component ref="foo"></my-component>
Access the component method:
<script>
this.$refs.foo.doSomething();
</script>

Say you have a child_method() in the child component:
export default {
methods: {
child_method () {
console.log('I got clicked')
}
}
}
Now you want to execute the child_method from parent component:
<template>
<div>
<button #click="exec">Execute child component</button>
<child-cmp ref="child"></child_cmp> <!-- note the ref="child" here -->
</div>
</template>
export default {
methods: {
exec () { //accessing the child component instance through $refs
this.$refs.child.child_method() //execute the method belongs to the child component
}
}
}
If you want to execute a parent component method from child component:
this.$parent.name_of_method()
NOTE: It is not recommended to access the child and parent component like this.
Instead as best practice use Props & Events for parent-child communication.
If you want communication between components surely use vuex or event bus
Please read this very helpful article

This is a simple way to access a component's methods from other component
// This is external shared (reusable) component, so you can call its methods from other components
export default {
name: 'SharedBase',
methods: {
fetchLocalData: function(module, page){
// .....fetches some data
return { jsonData }
}
}
}
// This is your component where you can call SharedBased component's method(s)
import SharedBase from '[your path to component]';
var sections = [];
export default {
name: 'History',
created: function(){
this.sections = SharedBase.methods['fetchLocalData']('intro', 'history');
}
}

Using Vue 3:
const app = createApp({})
// register an options object
app.component('my-component', {
/* ... */
})
....
// retrieve a registered component
const MyComponent = app.component('my-component')
MyComponent.methods.greet();
https://v3.vuejs.org/api/application-api.html#component

Here is a simple one
this.$children[indexOfComponent].childsMethodName();

I am not sure is it the right way but this one works for me.
First import the component which contains the method you want to call in your component
import myComponent from './MyComponent'
and then call any method of MyCompenent
myComponent.methods.doSomething()

Declare your function in a component like this:
export default {
mounted () {
this.$root.$on('component1', () => {
// do your logic here :D
});
}
};
and call it from any page like this:
this.$root.$emit("component1");

If you're using Vue 3 with <script setup> sugar, note that internal bindings of a component are closed (not visible from outside the component) and you must use defineExpose(see docs) to make them visible from outside. Something like this:
<script setup lang="ts">
const method1 = () => { ... };
const method2 = () => { ... };
defineExpose({
method1,
method2,
});
</script>
Since
Components using are closed by default

Sometimes you want to keep these things contained within your component. Depending on DOM state (the elements you're listening on must exist in DOM when your Vue component is instantiated), you can listen to events on elements outside of your component from within your Vue component. Let's say there is an element outside of your component, and when the user clicks it, you want your component to respond.
In html you have:
Launch the component
...
<my-component></my-component>
In your Vue component:
methods() {
doSomething() {
// do something
}
},
created() {
document.getElementById('outsideLink').addEventListener('click', evt =>
{
this.doSomething();
});
}

I have used a very simple solution. I have included a HTML element, that calls the method, in my Vue Component that I select, using Vanilla JS, and I trigger click!
In the Vue Component, I have included something like the following:
<span data-id="btnReload" #click="fetchTaskList()"><i class="fa fa-refresh"></i></span>
That I use using Vanilla JS:
const btnReload = document.querySelector('[data-id="btnReload"]');
btnReload.click();