I have this component which has a v-model directive:
<my-component v-model="someData.someProp"></my-component>
Now, I'd like to be able to watch this piece of data inside the component and make changes based on this model changing via outside influences. So here's what I tried and it's not working:
watch : {
value (newVal, oldVal) {
// ...
}
}
It seems like it should work, or something comparable should be out there, but I just can't find it right now.
EDIT:
The most common answers I found and provided center on using the watcher to watch the data as if it's inside the parent component - but I'd like to watch it inside the child component without concern of what's going on in the parent.
I'm able to work around this by not using v-model and using simple named properties such as :my-data="someData.someProp" at which point I can successfully watch a myData variable inside the child component. I can also use #input to set the data back in the parent component if it's changed from within. But v-model is shorter and if there's a way to use that instead of a workaround that would be preferable.
From what I understand you are trying to pass a prop to your child component from your parent one and watch it in your child.
Assuming you have something like this in your parent:
<div>
<my-component v-model="someData.someProp"></my-component>
</div>
I understand you are getting undefined for that prop when you watch it, which is normal because you should pass it like this:
<my-component :myValue="someData.someProp"></my-component>
Then you should have access to the prop trought this.myValue.
If someData.someProp changes on the parent component it will automatically reflect on the child one.
Again this is what I could understand from your explanation and the amount of code you provided.
Related
I am currently working on a project that has a component structure like follows
Parent component that contains items
This component has a v-for over this.items.
That v-for has a
ChildComponent contains a form that modifies properties of this.item via v-model for each property.
I was expecting, since VueJS does not support 2 way databinding by default, that ParentComponent would not be aware about changes that I make in ChildComponent.
However, since my ChildComponent is a modal dialog, I can see the changes that I make in ChildComponent are reflected in ParentComponent.
As much as I like what I see, I don't understand it...
Could someone shed a light on this for me?
Assuming that I have this component below:
<c-attachs v-for="item in attachs" v-bind:path="item.path"></c-attachs>
And try to edit some property directly from some method, such as:
methods: {
changeProp: function ()
{
this.path = 'myNewString';
}
}
Vuejs warns on the console with the message:
Avoid mutating a prop directly since the value will be overwritten whenever the parent component re-renders
But... if I set "v-bind:allprops="item" and edit property directly through "allprops" object (such as code below), it works fine without error. My doubt is... Is this the correct way to edit property on events without using v-model?
this.allprops.path = 'myNewString';
There is no correct way to edit props, because you are not supposed to edit them.
Every component should have complete control over its own data. That keeps behavior easy to reason about. Items that are passed to children as props should be considered read-only, so that the owner of those items retains control. That is why Vue has events.
When something happens in a component that should affect data that the component doesn't own, the component should issue an event so that the owner of the data item can handle it. If the owner of the data item changes its value, that change will flow down through the props.
I am trying to pass down a initial value to a select input bound by v-model. I cannot figure out why this doesn't work:
props: ['team'],
data() {
form: {
data: {
country: this.team.country
}
}
}
The form.data.country is undefined. Although, the props data is actually passed down. I can access it with Vue Devtools like $vm0.team.country and I can print other data from the props. However, it is not registred in the data().
Also, when trying to debug using mounted(), the property, team, is not defined.
mounted() {
console.log(this.team);
}
But, as I stated earlier, it is defined when the template is rendered, and can be used like this.
<input class="input" type="text" name="name" :value="team.name" disabled>
Why is the properties I am passing not beinged recognized in data()?
The asynchronous loading is not the problem. Even if team is hardcoded above, it's still undefined when data is created in the component. (The component needs to be created before the root Vue that passes the prop.)
There is, perhaps someone will correct me, never a good reason to reference props in your data. Something is either data (the current component knows where to find what it wants) or it's a prop (the component will let it's context supply the info).
Then, as you've discovered, your data is created once. Vue watches everything for changes, but you're vulnerable to changes of the root value. If the thing referenced as a value when data is created, changes, the reactive pipe is broken. The answer to this is the store pattern. You watch a variable in global scope, that never gets replaced, even though it's contents may change.
code
The props data was asynced loaded by the parent. This was suggested in a comment by #Bert
I have a simple component hierarchy, in which there is one parent component, which contains the following template <div><component :is="current"></component></div> and two child components, which are dynamically 'switched' out, via the value of current.
The logic for the 'switching' of components is being handled in the parent component. However, when I try to execute a method in the second child component (in response to an event emitted from the first child component, being listened to in the parent component, and altering the value of current in the parent component) through the mounted lifecycle hook, the expected result is not observed.
Essentially, I cannot find a decent way of invoking a child component's methods when that component is 'switched' in as the current component in the parent component.
I have realistically looked at using the $refs and $childrenproperties on the instance, but these do not seem to be of any assistance. I have also reasoned using the event system. I usually 'define' an event listener in the mounted lifecycle hook, however, I refer to the 'issue' of using the lifecycle hooks
What is the usual approach to this situation?
There are two options that immediately come to mind for child components invoking methods on being the "current" child component:
1) Using the mounted lifecycle hook. In order for this to work, you must be using v-if in order to conditionally display the child component, otherwise the child component will not trigger the mounted lifecycle hook. Otherwise, if you're using v-show or some other mechanism for conditionally displaying the child component, the mounted hook will only ever trigger once.
2) Using watched properties. In lieu of the above, you could do something like the following:
<child-component :target_prop="current"></child-component>
Vue.component('child-component', {
. . .,
props: ['target_prop'],
watch: {
target_prop: function() {
if(this.target_prop == your_expected_value) {
//execute the desired method for this component
}
}
}
});
This is, of course, just a proof-of-concept example and there are plenty of alternative ways to use the watched properties to your advantage.
I've also heard of using a "bus" to handle inter-component communication, but I don't believe it would be any better than the above two solutions (and is arguably worse).
Personally, I prefer the mounted lifecycle hook approach, though there's the caveat that any "settings" or data in your child components will be lost on switching between them (although you could also emit a settings object on destruction and store/restore those settings as needed, but that could get messy). You'll have to make the final judgment on which approach better suits your needs and which consequences you're more comfortable dealing with.
I know in vue, I can use this.$parent to get the upper component in the vdom tree. But I'm expecting something different: to get the component that rendered the current component.
For instance, I have a component (named comp-container) with template:
<template>
<comp-a>
<comp-b></comp-b>
</comp-a>
</template>
And in comp-b the $parent would be an instance of comp-a not comp-container which I'm expecting.
My current aproach is traversing up with the $parent attribute until I find comp-b exists in $options.components. This method is working for now but seems quite ugly and breaks if comp-b is a globaly registered component. Is there an official way to do this?
Passing the parent template component via props as <comp-b :container="this"></comp-b> may do the job, but it's too verbose to be liked.
I'm not sure about the exact use case, but basically if there are slots involved (which I almost assume, because otherwise $parent will work fine), you can find the rendering component at:
this.$slots.default[0].context;
Basically, the context property of a slot is the rendering context (rendering component - i.e. the component who's template the component was rendered in).
Only tested with Vue 2