So I have the following piss of code in my child component
props: {
prop_accounts: Array,
prop_pushing_destination: String,
prop_selected_account: String,
prop_selected: Boolean,
shop_settings: Object,
name_of_selected_account_field: String
},
data() {
return {
accounts: this._.cloneDeep(this.prop_accounts),
pushing_destination: this._.cloneDeep(this.prop_pushing_destination),
selected_account: this._.cloneDeep(this.prop_selected_account),
selected: this._.cloneDeep(this.prop_selected)
}
},
The parent props pass all the props and all seams to work well but the parent is constantly sampling the backend for changes and if they acquire it updates the props of child and although I can see that props are changed the data stays the same now if I throw the data and use props directly all works well but I get the following warning
Avoid mutating a prop directly since the value will be overwritten whenever the parent component re-renders. Instead, use a data or computed property based on the prop's value. Prop being mutated: "selected_account"
There are two ways you could handle this: use the props directly and emit changes to the parent; or use computed properties to compute the value based on the data and props.
Emitting changes is probably what you want to do 99% of the time as any changes to the props either internal or external will change what your component is doing. Using computed props allows for changes to the props to be used only if the data hasn't been modified internally.
Computed props
props: {
defaultAccounts: Array,
defaultSelected: Boolean,
...
}
data: () => ({
customAccounts: null,
customSelected: null,
})
computed: {
accounts() {
return (this.customAccounts == null) ? this.defaultAccounts : this.customAccounts
},
selected() {
return (this.customSelected == null) ? this.defaultSelected : this.customSelected
}
}
You could even define setters on the computed props to set the value of the data properties.
Emit changes
Component:
props: {
accounts: Array,
selected: Boolean,
...
}
methods: {
accountsChanged(value) {
this.$emit('update:accounts', value)
},
selectedChanged(value) {
this.$emit('update:selected', value)
}
}
Where you use component:
<my-component :accounts.sync="accounts" :selected.sync="false"></my-component>
See Sync Modifier Documentation for more info.
I haven't tested this code so it may need tweaking to get it working correctly.
Related
I'm using Vue in vanilla JS and have a property defined in my data of type string which looks like this
data() {
return {
DimensionSetting: { type : String }
}
}
I have an element in my template that I want to toggle off when a value is passed into DimensionSetting however I can't figure out how I need to check for it in the v-if logic. I tried v-if="!this.DimensionSetting" and v-if="this.DimensionSetting === undefined" and v-if="this.DimensionSetting === null". None of these make the element visible when the value is empty. What do I need to do to properly check that kind of property?
It looks like you're incorrectly mixing a data property declaration with a props declaration.
If DimensionSetting is supposed to be a public property that receives values from a parent component, it should be declared under props:
export default {
props: {
DimensionSetting: {
type: String,
}
}
}
On the other hand, if DimensionSetting is supposed to be a local property, private to the component itself, then it should be returned from data(). There is no type field like there is for props declarations:
export default {
data() {
return {
DimensionSetting: ''
}
}
}
In either case, using the ! operator on the prop should be enough to check for an empty string:
<p v-if="!DimensionSetting">Empty</p>
demo
try adding,
data(){
return{
DimensionSetting: { type : String ,default:false}
}
}
and then v-if="!DimensionSetting"
I'm a newbie in Vuejs. I'm trying passing computed with param to props of child component but it's error.
This is my code:
<FloatingInput
:type="'text'"
:name="'username'"
:error="fieldError('username')"
>
<FloatingInput
:type="'password'"
:name="'password'"
:error="fieldError('password')"
>
And in the script:
computed: {
fieldError: {
get: function () {
return this.error[field]; // will return false or message error
},
set: function (field) {
this.error[field];
}
},
}
Computed properties are meant to be pure. This means that computed properties rely solely on the state of the component, and should not have side-effects. This allows Vue to only recalculate computed properties whenever the data they rely on changes. For this reason you can not call a computed property. You must use a method.
Luckily for you, what you want to do is just a key lookup in an object, so you can just use a data attribute and lookup the field.
<FloatingInput
type="text"
name="username"
:error="fieldErrors['username']"
>
data () {
fieldErrors: {}
},
methods: {
setFieldError(field, error) {
this.$set(this.fieldErrors, field, error);
}
}
Codepen Demo
I have a component which has an location object as props. The argument I passed in is locations[index] which is a selected item from a locations array.
However, the component cannot react when the index change. As you can see in the demo, the JSON change as you click the button, but the component cannot update.
What's the best way to make the component reactive?
Your location component populates the province and city data properties in the mounted hook only. When the location prop changes, the mounted hook will not be called again, so you are left with stale data.
Use a computed property instead:
computed: {
province() {
return this.location.province;
},
city() {
return this.location.city;
}
}
Updated codepen
If you really do require province and city to be data properties (and not computed properties) then you will need to watch the location prop to update the properties:
data() {
return {
province: null,
city: null
}
},
watch: {
location: {
immediate: true,
handler(loc) {
this.province = loc.province;
this.city = loc.city;
}
}
}
Nested items in your prop location won't be reactive, you'll need to use something like lodash deepClone :
<location :location.sync="_.deepClone(loc)"></location>
That's it, no need for watchers or anything else.
I have code like below
created () {
EventBus.$on('change',this.formated);
},
props: ['applicants',],
data() {
return {
values: [],
}
},
methods : {
formated (item) {
//some code here
}
}
I have some checkboxes in another component. I am trying to catch values of those checkboxes in this component. After catching those values I would like to filter the props applicants. I would like to find out which applicants have those values of checkboxes. Then I would like to pass them to values[]. Then I would like to iterate those values in HTML.
After reading the comments I believe this is what you need to do. You can use the prop as well as the data passed through the event bus in the formatted() method. You need to combine the two and set them to values. I have pasted code below. However, not knowing the structure of either two objects I can't help you further. This is just plain JavaScript. So probably you need something like Object.assign or the .filter or .map methods.
created () {
EventBus.$on('change',this.formatted);
},
props: ['applicants'],
data() {
return {
values: [],
}
},
methods : {
formatted (item) {
this.applicants // access the data from your prop
item // access the data from your event bus
this.values = someCombinationOf(this.applicants, item)
}
}
After setting values from the formatted () function you can iterate over it (for example with v-for). Whenever an event is emitted through the event bus this will update your component. Whenever the prop changes the component will be updated also.
How do I access $refs inside computed? It's always undefined the first time the computed property is run.
Going to answer my own question here, I couldn't find a satisfactory answer anywhere else. Sometimes you just need access to a dom element to make some calculations. Hopefully this is helpful to others.
I had to trick Vue to update the computed property once the component was mounted.
Vue.component('my-component', {
data(){
return {
isMounted: false
}
},
computed:{
property(){
if(!this.isMounted)
return;
// this.$refs is available
}
},
mounted(){
this.isMounted = true;
}
})
I think it is important to quote the Vue js guide:
$refs are only populated after the component has been rendered, and they are not reactive. It is only meant as an escape hatch for direct child manipulation - you should avoid accessing $refs from within templates or computed properties.
It is therefore not something you're supposed to do, although you can always hack your way around it.
If you need the $refs after an v-if you could use the updated() hook.
<div v-if="myProp"></div>
updated() {
if (!this.myProp) return;
/// this.$refs is available
},
I just came with this same problem and realized that this is the type of situation that computed properties will not work.
According to the current documentation (https://v2.vuejs.org/v2/guide/computed.html):
"[...]Instead of a computed property, we can define the same function as a method. For the end result, the two approaches are indeed exactly the same. However, the difference is that computed properties are cached based on their reactive dependencies. A computed property will only re-evaluate when some of its reactive dependencies have changed"
So, what (probably) happen in these situations is that finishing the mounted lifecycle of the component and setting the refs doesn't count as a reactive change on the dependencies of the computed property.
For example, in my case I have a button that need to be disabled when there is no selected row in my ref table.
So, this code will not work:
<button :disabled="!anySelected">Test</button>
computed: {
anySelected () {
if (!this.$refs.table) return false
return this.$refs.table.selected.length > 0
}
}
What you can do is replace the computed property to a method, and that should work properly:
<button :disabled="!anySelected()">Test</button>
methods: {
anySelected () {
if (!this.$refs.table) return false
return this.$refs.table.selected.length > 0
}
}
For others users like me that need just pass some data to prop, I used data instead of computed
Vue.component('my-component', {
data(){
return {
myProp: null
}
},
mounted(){
this.myProp= 'hello'
//$refs is available
// this.myProp is reactive, bind will work to property
}
})
Use property binding if you want. :disabled prop is reactive in this case
<button :disabled="$refs.email ? $refs.email.$v.$invalid : true">Login</button>
But to check two fields i found no other way as dummy method:
<button :disabled="$refs.password ? checkIsValid($refs.email.$v.$invalid, $refs.password.$v.$invalid) : true">
{{data.submitButton.value}}
</button>
methods: {
checkIsValid(email, password) {
return email || password;
}
}
I was in a similar situation and I fixed it with:
data: () => {
return {
foo: null,
}, // data
And then you watch the variable:
watch: {
foo: function() {
if(this.$refs)
this.myVideo = this.$refs.webcam.$el;
return null;
},
} // watch
Notice the if that evaluates the existence of this.$refs and when it changes you get your data.
What I did is to store the references into a data property. Then, I populate this data attribute in mounted event.
data() {
return {
childComps: [] // reference to child comps
}
},
methods: {
// method to populate the data array
getChildComponent() {
var listComps = [];
if (this.$refs && this.$refs.childComps) {
this.$refs.childComps.forEach(comp => {
listComps.push(comp);
});
}
return this.childComps = listComps;
}
},
mounted() {
// Populates only when it is mounted
this.getChildComponent();
},
computed: {
propBasedOnComps() {
var total = 0;
// reference not to $refs but to data childComps array
this.childComps.forEach(comp => {
total += comp.compPropOrMethod;
});
return total;
}
}
Another approach is to avoid $refs completely and just subscribe to events from the child component.
It requires an explicit setter in the child component, but it is reactive and not dependent on mount timing.
Parent component:
<script>
{
data() {
return {
childFoo: null,
}
}
}
</script>
<template>
<div>
<Child #foo="childFoo = $event" />
<!-- reacts to the child foo property -->
{{ childFoo }}
</div>
</template>
Child component:
{
data() {
const data = {
foo: null,
}
this.$emit('foo', data)
return data
},
emits: ['foo'],
methods: {
setFoo(foo) {
this.foo = foo
this.$emit('foo', foo)
}
}
}
<!-- template that calls setFoo e.g. on click -->