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.$options.computed.xyz
},
childProprty1() {},
childProprty2() {}
}
}
For me it happened because I wrote method: instead of methods: (plural). It's a silly mistake but it can happen :)
In my case it was the methods: { } I had put the } before my method functions so for example I had it like this methods: { function , function }, function, function so some of the functions that were out of the curly braces were not included inside the methods function.
In my component I'm trying to access the getters from my auth module.
This is the getter function in store/auth.js
getters: {
isAuthenticated: (state) => !!state.token,
},
And here is how I trying to access and display this data
// html in template of component
<span
v-if='this.isAuthenticated'
class='font-weight-bold grey--text text--darken-3'>
Hello
</span>
-------------------
// computed properties of component
computed: {
...mapGetters([
'auth/isAuthenticated',
]),
},
and in the devtools this is the error i am getting
' Property or method "isAuthenticated" is not defined on the instance but referenced during render.'
I'm really not sure why and not sure how to access this data, in the Vue debugger i can see that the getter works and is returning true.
I have tried other ways to access the data such as
isAuthenticated: () => this.$store.getters.isAuthenticated // and this.$store.getters.auth.isAuthenticated
but this gives a different error saying typeError: Cannot read property '$store' of undefined when i try to access the computed function in the template.
This is really annoying because to my knowledge i am correctly trying to access the store and its not working.
An explanation would be greatly appreciated. Thanks.
You have two different errors in your two different approaches. Let's see your first approach first:
---
<span
v-if='this.isAuthenticated'
---
computed: {
...mapGetters([
'auth/isAuthenticated',
]),
}
---
Here, your problem is that you're trying to map a namespaced getter, but trying to access the attribute without the namespace. You can work around this by using an object parameter for the mapGetters function:
computed: {
...mapGetters({
isAuthenticated: 'auth/isAuthenticated',
}),
}
In your second approach, you almost get it right, but you run into a different set of issues:
isAuthenticated: () => this.$store.getters.isAuthenticated
First of all, if the module is namespaced, the correct way to access the getter would be this.$store.getters['auth/isAuthenticated'].
Apart from that, you should not use arrow functions in Vue components, since the this context is lost (it points to the function rather than the Vue instance). You need to use a regular function.
Combining both of these fixes, the result would be:
isAuthenticated(){
return this.$store.getters['auth/isAuthenticated']
}
My method in vue looks like this :
methods: {
setDate: async function () {
console.log(this.modal)
}
}
I want to change it to an arrow function. I tried like this :
methods: {
setDate: async () => {
console.log(this.modal)
}
}
There exist error like this :
Cannot read property 'modal' of undefined
How can I solve this problem?
use function directly like
methods: {
async setDate() {
console.log(this.modal)
}
}
You are facing this error because an arrow function wouldn't bind this to the vue instance for which you are defining the method. The same would happen if you were to define computed properties using an arrow function.
Don’t use arrow functions on an instance property or callback e.g.
vm.$watch('a', newVal => this.myMethod())
As arrow functions are bound to the parent context, this will not be the Vue instance as you’d expect and this.myMethod will be undefined.
You can read about it here.
This link https://michaelnthiessen.com/this-is-undefined/ says the following:
"An arrow function uses what is called lexical scoping. We'll get into this more in a bit, but it basically means that the arrow function takes this from it's context.
If you try to access this from inside of an arrow function that's on a Vue component, you'll get an error because this doesn't exist!
So in short, try to avoid using arrow functions on Vue components. It will save you a lot of headaches and confusion."
I want to use jointjs to achieve a demand, like this:
paper.on('cell:pointerdblclick', function(cellView) {}). In vue, what should i do?
ReferenceError: cellView is not defined
<script>
export default {
mounted(){},
methods: {
registerDoubleClickEvent()
{this.paper.on('cell:pointerdblclick',
this.connectTwoObject(cellView))},
connectTwoObject(cellView){alert('1234');},
}}
</script>
Thanks in advance!
As i understood from the question, you want to pass the first argument of callback to your method. Seems like your syntax is wrong. You are just calling your method with an undefined variable. To access this variable try the code bellow (arrow function is used to save the context). Also, I believe you have connectTwoObject method defined in your methods.
export default {
mounted() {},
methods: {
registerDoubleClickEvent() {
this.paper.on('cell:pointerdblclick', cellView =>
this.connectTwoObject(cellView),
)
},
},
}
Can any one guide or suggest how to resolve this below issue.
Use Case: Trying to implement notification component
Scenario: I am trying to call a method or change the state of the data on triggering of event in Vue.
I have defined the event listener on mounted function and trying to access one of the method.
Basically, the alert within event function is getting triggered, where as alert inside method is not getting triggered, and even any data manipulation is not executing even with in event function.
Where am i missing? is it incorrect to alter state within Event listener?
Basically i am trying to implement notification feature which automatically disappear after few seconds
Any help is appreciated.
Thanks,
Girish
There is another reason,this inside callback function is not Vue component. You can assign var self = this and use inside the callback, or use arrow function.
mounted: function () {
var self = this
EventBus.$on('show', function () {
self.test()
self.show = true
})
},
methods: {
test () {
console.log('Inside methods')
}
}
I believe your problem is the spelling error instead of
method: {}
, use methods: {}
Example:
Error.
method: {
test: function () {
alert('Inside Method');
}
correct.
methods: {
test: function () {
alert('inside method);
}
}
I know it does not have much to do with the question, but be careful when using the event bus, it would be as if you had a speaker, and shouted in the middle of a crowd the name of a person.
Example:
eventbus says Hamilton in the midst of a crowd of 10,000 people.
How many Hamiltons can you have in the middle of this crowd? Use something more specific, such as parent-child communication, avoid using the event bus.