I am new to Vue. So I gotta tell ya, what I am doing here is working, but I am also get a dev tools error.
[Vue warn]: v-on with no argument expects an object value.
Now, I get WHY it is telling me this, but when I try to fix it in a couple of ways, I get a number of errors. What I am wondering is how would I resolve this properly. I also want to stress what the code is doing IS working as expected on the frontend. Just not proper Vue I would like to resolve
TEMPLATE
<div v-if="message.type === 'message'">
<chat-message v-on="playMessageNotificationSound()"
:message="message"/>
</div>
<div v-else-if="message.type === 'notification'">
<div v-show="this.$store.state.notifications.enterLeave === 'true'">
<chat-notification v-on="playNotificationSound()" :message="message" />
</div>
</div>
SCRIPT
methods: {
playMessageNotificationSound() {
if (this.$store.state.notifications.messagesound === 'true' ) {
var audio = new Audio('https://chat-cdn.levelupchat.com/chat-sounds/whisper.mp3');
audio.volume = 0.4;
audio.play();
}
},
playNotificationSound () {
if (this.$store.state.notifications.enterLeaveSound === 'true' ) {
var audio = new Audio('https://chat-cdn.levelupchat.com/chat-sounds/message.mp3');
audio.volume = 0.4;
audio.play();
}
},
v-on is a directive to listen to DOM events and run some JavaScript when they’re triggered.
You can't use it empty instead need to bind an event handler .
For example
<button v-on:click="say('hi')">Say hi</button>
where
methods: {
say: function (message) {
alert(message)
}
}
For more info : https://v2.vuejs.org/v2/guide/events.html#Listening-to-Events
The v-on directive is intended for binding event listeners, but you're not actually trying to listen to any events, so you're misusing the v-on directive, leading to the warning you observed.
When Vue loads <chat-message v-on="playNotificationSound()">, it calls playNotificationSound(), expecting a return value to assign to v-on. Since playNotificationSound() is called when chat-message and chat-notification is rendered, it only appears to work as intended (the sound coincides with the chat message/notification).
However, there are no events to be handled here, so v-on should not be used. The call to playNotificationSound() should perhaps be moved into a watcher on message.type:
export default {
watch: {
'message.type'(messageType) {
if (messageType === 'message') {
this.playMessageNotificationSound()
} else if (messageType === 'notification' && this.$store.state.notifications.enterLeave === 'true') {
this.playNotificationSound()
}
}
}
}
in react and jsx I would use curly braces to pass nested functions and their params, as parameters. but since there is this quote syntax in vue js, I am confused.
what I'm trying to do is something like this:
<span #click="myFirstFunction( ()=> console.log('param') )" />
myFirstFunction(code){
code();
}
actually, this is the simplified version
what I'm trying to do is to save that code in an state and run it in other situations
but this doesn't seem to work.
Actually, your syntax is correct. But in your simple example, you are trying to access a property or a data which is not defined. You may think console is a global object it should be accessed from anywhere, but no. You can only access component properties (data, methods, etc.) from the template in VUE. So you should do something like below to access the console or any other global object:
data() {
return {
console: Object,
};
},
created() {
this.console = console;
},
SandBox
You should do either
<span #click="() => console.log('param')" />
or
<span #click="myFirstFunction" />
myFirstFunction should be defined as a method.
methods: {
myFirstFunction() {
// your function
}
}
The following code has been written to handle an event after a button click
var MainTable = Vue.extend({
template: "<ul>" +
"<li v-for='(set,index) in settings'>" +
"{{index}}) " +
"{{set.title}}" +
"<button #click='changeSetting(index)'> Info </button>" +
"</li>" +
"</ul>",
data: function() {
return data;
}
});
Vue.component("main-table", MainTable);
data.settingsSelected = {};
var app = new Vue({
el: "#settings",
data: data,
methods: {
changeSetting: function(index) {
data.settingsSelected = data.settings[index];
}
}
});
But the following error occurred:
[Vue warn]: Property or method "changeSetting" is not defined on the instance but referenced during render. Make sure to declare reactive data properties in the data option. (found in <MainTable>)
Problem
[Vue warn]: Property or method "changeSetting" is not defined on the instance but referenced during render. Make sure to declare reactive data properties in the data option. (found in <MainTable>)
The error is occurring because the changeSetting method is being referenced in the MainTable component here:
"<button #click='changeSetting(index)'> Info </button>" +
However the changeSetting method is not defined in the MainTable component. It is being defined in the root component here:
var app = new Vue({
el: "#settings",
data: data,
methods: {
changeSetting: function(index) {
data.settingsSelected = data.settings[index];
}
}
});
What needs to be remembered is that properties and methods can only be referenced in the scope where they are defined.
Everything in the parent template is compiled in parent scope; everything in the child template is compiled in child scope.
You can read more about component compilation scope in Vue's documentation.
What can I do about it?
So far there has been a lot of talk about defining things in the correct scope so the fix is just to move the changeSetting definition into the MainTable component?
It seems that simple but here's what I recommend.
You'd probably want your MainTable component to be a dumb/presentational component. (Here is something to read if you don't know what it is but a tl;dr is that the component is just responsible for rendering something – no logic). The smart/container element is responsible for the logic – in the example given in your question the root component would be the smart/container component. With this architecture you can use Vue's parent-child communication methods for the components to interact. You pass down the data for MainTable via props and emit user actions from MainTable to its parent via events. It might look something like this:
Vue.component('main-table', {
template: "<ul>" +
"<li v-for='(set, index) in settings'>" +
"{{index}}) " +
"{{set.title}}" +
"<button #click='changeSetting(index)'> Info </button>" +
"</li>" +
"</ul>",
props: ['settings'],
methods: {
changeSetting(value) {
this.$emit('change', value);
},
},
});
var app = new Vue({
el: '#settings',
template: '<main-table :settings="data.settings" #change="changeSetting"></main-table>',
data: data,
methods: {
changeSetting(value) {
// Handle changeSetting
},
},
}),
The above should be enough to give you a good idea of what to do and kickstart resolving your issue.
Should anybody land with the same silly problem I had, make sure your component has the 'data' property spelled correctly. (eg. data, and not date)
<template>
<span>{{name}}</span>
</template>
<script>
export default {
name: "MyComponent",
data() {
return {
name: ""
};
}
</script>
In my case the reason was, I only forgot the closing
</script>
tag.
But that caused the same error message.
If you're experiencing this problem, check to make sure you don't have
methods: {
...
}
or
computed: {
...
}
declared twice
It's probably caused by spelling error
I got a typo at script closing tag
</sscript>
Remember to return the property
Another reason of seeing the Property "search" was accessed during render but is not defined on instance is when you forget to return the variable in the setup(){} function
So remember to add the return statement at the end:
export default {
setup(){
const search = ref('')
//Whatever code
return {search}
}
}
Note: I'm using the Composition API
Adding my bit as well, should anybody struggle like me, notice that methods is a case-sensitive word:
<template>
<span>{{name}}</span>
</template>
<script>
export default {
name: "MyComponent",
Methods: {
name() {return '';}
}
</script>
'Methods' should be 'methods'
If you use two times vue instance. Then it will give you this error. For example in app.js and your own script tag in view file. Just use one time
const app = new Vue({
el: '#app',
});
I got this error when I tried assigning a component property to a state property during instantiation
export default {
props: ['value1'],
data() {
return {
value2: this.value1 // throws the error
}
},
created(){
this.value2 = this.value1 // safe
}
}
My issue was I was placing the methods inside my data object. just format it like this and it'll work nicely.
<script>
module.exports = {
data: () => {
return {
name: ""
}
},
methods: {
myFunc() {
// code
}
}
}
</script>
In my case, I wrote it as "method" instead of "methods". So stupid. Wasted around 1 hour.
Some common cases of this error
Make sure your component has the data property spelled correctly
Make sure your template is bot defined within another component’s template.
Make sure you defined the variable inside data object
Make sure your router name in string
Get some more sollution
It is most likely a spelling error of reserved vuejs variables. I got here because I misspelled computed: and vuejs would not recognize my computed property variables. So if you have an error like this, check your spelling first!
I had two methods: in the <script>, goes to show, that you can spend hours looking for something that was such a simple mistake.
if you have any props or imported variables (from external .js file) make sure to set them properly using created like this;
make sure to init those vars:
import { var1, var2} from './constants'
//or
export default {
data(){
return {
var1: 0,
var2: 0,
var3: 0,
},
},
props: ['var3'],
created(){
this.var1 = var1;
this.var2 = var2;
this.var3 = var3;
}
In my case it was a property that gave me the error, the correct writing and still gave me the error in the console. I searched so much and nothing worked for me, until I gave him Ctrl + F5 and Voilá! error was removed. :'v
Look twice the warning : Property _____ was accessed during render but is not defined on instance.
So you have to define it ... in the data function for example which commonly instantiate variables in a Vuejs app. and, it was my case and that way the problem has been fixed.
That's all folk's !
In my case, I forgot to add the return keyword:
computed: {
image(){
this.productVariants[this.selectedVariant].image;
},
inStock(){
this.productVariants[this.selectedVariant].quantity;
}
}
Change to:
computed: {
image(){
return this.productVariants[this.selectedVariant].image;
},
inStock(){
return this.productVariants[this.selectedVariant].quantity;
}
}
In my case due to router name not in string:
:to="{name: route-name, params: {id:data.id}}"
change to router name in string:
:to="{name: 'router-name', params: {id:data.id}}"
In my case I was trying to pass a hard coded text value to another component with:
ChildComponent(:displayMode="formMode")
when it should be:
ChildComponent(:displayMode="'formMode'")
note the single quotes to indicate text instead of calling a local var inside the component.
If you're using the Vue3 <script setup> style, make sure you've actually specified setup in the opening script tag:
<script setup>
I had lapsed into old habits and only created a block with <script>, but it took a while to notice it.
https://v3.vuejs.org/api/sfc-script-setup.html
Although some answers here maybe great, none helped my case (which is very similar to OP's error message).
This error needed fixing because even though my components rendered with their data (pulled from API), when deployed to firebase hosting, it did not render some of my components (the components that rely on data).
To fix it (and given you followed the suggestions in the accepted answer), in the Parent component (the ones pulling data and passing to child component), I did:
// pulled data in this life cycle hook, saving it to my store
created() {
FetchData.getProfile()
.then(myProfile => {
const mp = myProfile.data;
console.log(mp)
this.$store.dispatch('dispatchMyProfile', mp)
this.propsToPass = mp;
})
.catch(error => {
console.log('There was an error:', error.response)
})
}
// called my store here
computed: {
menu() {
return this.$store.state['myProfile'].profile
}
},
// then in my template, I pass this "menu" method in child component
<LeftPanel :data="menu" />
This cleared that error away. I deployed it again to firebase hosting, and voila!
Hope this bit helps you.
It seems there are many scenarios that can trigger this error. Here's another one which I just resolved.
I had the variable actionRequiredCount declared in the data section, but I failed to capitalize the C in Count when passing the variable as a params to a component.
Here the variable is correct:
data: () => {
return{
actionRequiredCount: ''
}
}
In my template it was incorrect (notd the no caps c in "count"):
<MyCustomModule :actionRequiredCount="actionRequiredcount"/>
Hope this helps someone.
Most people do have an error here because of:
a typo or something that they forgot to declare/use
the opposite, did it in several places
To avoid the typo issues, I recommend always using Vue VSCode Snippets so that you don't write anything by hand by rather use vbase, vdata, vmethod and get those parts generated for you.
Here are the ones for Vue3.
You can of course also create your own snippets by doing the following.
Also make sure that you're properly writing all the correct names as shown here, here is a list:
data
props
computed
methods
watch
emits
expose
As for the second part, I usually recommend either searching the given keyword in your codebase. So like cmd + f + changeSetting in OP's case to see if it's missing a declaration somewhere in data, methods or alike.
Or even better, use an ESlint configuration so that you will be warned in case you have any kind of issues in your codebase.
Here is how to achieve such setup with a Nuxt project + ESlint + Prettier for the most efficient way to prevent bad practices while still getting a fast formatting!
One other common scenario is:
You have a component (child) extending another component (parent)
You have a property or a method xyz defined under methods or computed on the parent component.
Your are trying to use parent's xyz, but your child component defines its own methods or computed
Sample code with the problem
// PARENT COMPONENT
export default {
computed() {
abc() {},
xyz() {} // <= needs to be used in child component
},
...
}
// CHILD COMPONENT
export default {
extends: myParentComponent,
computed() {
childProprty1() {},
childProprty2() {}
}
}
The solution
In this case you will need to redefine your xyz computed property under computed
Solution 1:
Redefine xyz and copy the code from the parent component
// CHILD COMPONENT
export default {
extends: myParentComponent,
computed() {
xyz() {
// do something cool!
},
childProprty1() {},
childProprty2() {}
}
}
Solution 2
Redefine xyz property reusing parent component code (no code redundancy)
// CHILD COMPONENT
export default {
extends: myParentComponent,
computed() {
xyz() {
return this.$parent.$options.computed.xyz
},
childProprty1() {},
childProprty2() {}
}
}
For me it happened because I wrote method: instead of methods: (plural). It's a silly mistake but it can happen :)
In my case it was the methods: { } I had put the } before my method functions so for example I had it like this methods: { function , function }, function, function so some of the functions that were out of the curly braces were not included inside the methods function.
I have some code similar to below:
<some_component v-model="some_value" />
{{ some_value }}
In my script code I have the following:
...
data() {
return {
some_value: 'initial'
};
},
...
watch: {
some_value(new_value, old_value) {
// Small subset of code, actual code does much more than this
if (new_value === 'some_new_value') {
this.some_value = 'can not use that value';
}
}
},
...
So everything seems be functioning fine, until I try to change the value I'm watching from within the watcher itself. I would expect the watcher to fire again, but it doesn't and although value of the v-model changes, it does't change in the UI.
I tried using this.$forceUpdate() before and after change but it didn't seem to work.
Can anyone tell me what I'm doing wrong here?
You shouldn't update the value you're watching in its watcher, but if you have no other choice you can use $nextTick
some_value(new_value, old_value) {
// Small subset of code, actual code does much more than this
if (new_value === 'some_new_value') {
this.$nextTick(() => {
this.some_value = 'can not use that value';
})
}
}
another way to do it (and the best in my opinion) is directly overriding v-model.
as you may know, v-model="some_value" is shorthand for :value="some_value" and #input="some_value=$event". so you can do what you're trying to like this:
<some-component
:value="some_value"
#input="some_value=some_method($event)"
/>
How do you bind a method result to a v-model with Vue.js?
example :
<someTag v-model="method_name(data_attribute)"></someTag>
I can't make it work for some reason.
Thank you.
Years later, with more experience, I found out that is it easier to bind :value instead of using v-model. Then you can handle the update by catching #change.
Edit (per request):
<input :value="myValue" #change="updateMyValue">
...
methods: {
updateMyValue (event) {
myValue = event.target.value.trim() // Formatting example
}
}
And in a child component:
// ChildComponent.vue
<template>
<button
v-for="i in [1,2,3]">
#click="$emit('change', i) />
</template>
// ParentComponent.vue
<template>
<child-component #change="updateMyValue" />
</template>
<script>
import ChildComponent from './child-component'
export default {
components: {
ChildComponent
},
data () {
return {
myvalue: 0
}
},
methods: {
updateMyValue (newValue) {
this.myvalue = newValue
}
}
}
</script>
v-model expressions must have a get and set function. For most variables this is pretty straight forward but you can also use a computed property to define them yourself like so:
data:function(){
return { value: 5 }
},
computed: {
doubleValue: {
get(){
//this function will determine what is displayed in the input
return this.value*2;
},
set(newVal){
//this function will run whenever the input changes
this.value = newVal/2;
}
}
}
Then you can use <input v-model="doubleValue"></input>
if you just want the tag to display a method result, use <tag>{{method_name(data_attribute)}}</tag>
Agree with the :value and #change combination greenymaster.
Even when we split the computed property in get/set, which is help, it seems very complicated to make it work if you require a parameter when you call for get().
My example is a medium sized dynamic object list, that populates a complex list of inputs, so:
I can't put a watch easily on a child element, unless I watch the entire parent list with deep, but it would require more complex function to determine which of the innter props and/or lists changed and do what fromthere
I can't use directly a method with v-model, since, it works for providing a 'get(param)' method (so to speak), but it does not have a 'set()' one
And the splitting of a computed property, have the same problem but inverse, having a 'set()' but not a 'get(param)'