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.
Vue documentation gives an example of simple state management, for a single-file app:
const sourceOfTruth = {}
const vmA = new Vue({
data: sourceOfTruth
})
const vmB = new Vue({
data: sourceOfTruth
})
How to use the same mechanism for components?
I tried to move this concept of a minimal state manager to components in a codesandbox.io sandbox. It did not work and the more meaningful error, I believe, is
The "data" option should be a function that returns a per-instance value in component definitions.
Does this mean that components must be completely standalone and cannot rely on data managed outside of them?
try this Sandbox updated
in dataMaster.js
var store = {
state: {
message: "Hello!"
}
};
module.exports = store;
and component.vue
<template>
<div>
<h1>{{sharedState}}</h1>
</div>
</template>
<script>
import store from "./dataMaster";
export default {
name: "HelloWorld",
data() {
return {
privateState: {},
sharedState: store.state
};
}
};
</script>
The "data" option should be a function that returns a per-instance value in component definitions
It means that the data property you define in the component must be a function, and that function should return a per-instance value. You should, not any must here, and it can be tricked.
About the error, you got the error not because of state management, but because you forgot to export the function in dataMaster.js, so you couldn't import and use it in HelloWorld.vue. You got the error because you didn't return a function, that was the function part, not per-instance or anything related to state management.
To do the trick that I think you want, here it is: https://codesandbox.io/s/unruffled-carson-l3oui. You change the same source of truth directly from components, yet without tools like VueX or something. But it's tricky and is exactly what the error try to avoid, return a per-instance value. I don't know what the advantages and disadvantages of it yet, but at the end of the day, I think to do state management, we should use the standard recommended way from the prior people, like VueX, etc, just choose one from tons of them.
// dataMaster.js
const data = {
msg: "hello From dataMaster"
};
export default function dataMaster() {
return data // this is not "per-instance", they're the same across all instances
}
//Hello.vue
<template>
<div>
{{msg}}
<button #click="change">Change</button>
</div>
</template>
<script>
import dataMaster from "./dataMaster.js";
export default {
name: "HelloWorld",
data: dataMaster,
methods: {
change() {
this.msg = this.msg === "message1" ? "message2" : "message1";
}
}
};
</script>
"data" option should be a function, cause pure object could make data mess up. e.g when "sourceOfTruth" modified by componentA but you are focus on componentB, and you will confused. so please use "vuex" or "eventbus".
If you want to manage all data from global state. you should search and learn Vuex and Store Management.
Maybe using "Event Bus" is better for you example.
And you're wrong with this code, we always need to export the code.
export default function dataMaster() {
return {
msg: "hello from dataMaster"
};
}
What's the difference between this code:
new Vue({
data () {
return {
text: 'Hello, World'
};
}
}).$mount('#app')
and this one:
new Vue({
el: '#app',
data () {
return {
text: 'Hello, World'
};
}
})
I mean what's the benefit in using .$mount() instead of el or vice versa?
$mount allows you to explicitly mount the Vue instance when you need to. This means that you can delay the mounting of your vue instance until a particular element exists in your page or some async process has finished, which can be particularly useful when adding vue to legacy apps which inject elements into the DOM, I've also used this frequently in testing (See Here) when I've wanted to use the same vue instance across multiple tests:
// Create the vue instance but don't mount it
const vm = new Vue({
template: '<div>I\'m mounted</div>',
created(){
console.log('Created');
},
mounted(){
console.log('Mounted');
}
});
// Some async task that creates a new element on the page which we can mount our instance to.
setTimeout(() => {
// Inject Div into DOM
var div = document.createElement('div');
div.id = 'async-div';
document.body.appendChild(div);
vm.$mount('#async-div');
},1000)
Here's the JSFiddle: https://jsfiddle.net/79206osr/
According to the Vue.js API docs on vm.$mount(), the two are functionally the same, except that $mount can (optionally) be called without an element selector, which causes the Vue model to be rendered separate from the document (so it can be appended later). This example is from the docs:
var MyComponent = Vue.extend({
template: '<div>Hello!</div>'
})
// create and mount to #app (will replace #app)
new MyComponent().$mount('#app')
// the above is the same as:
new MyComponent({ el: '#app' })
// or, render off-document and append afterwards:
var component = new MyComponent().$mount()
document.getElementById('app').appendChild(component.$el)
In the example you provide, I don't believe there is really much difference or benefit. However, in other situations there may be a benefit. (I have never encountered situations like the following).
With $mount() you have more flexibility what element it will be
mounted on if that were to ever be necessary.
Similarly you if for some reason you need to instantiate the
instance before you actually know what element it will be mounted on
(maybe an element that is created dynamically) then you could mount
it later using vm.$mount()
Following along with the above you could use also use mount when you
need to make a decision before hand which element to mount to
assuming that there may be two or more possibilities.
Something like...
if(document.getElementById('some-element') != null){
// perform mount here
}
Top answer is good enough. just left a comment here as I don't have enough reputation points. Alternativley:
setTimeout(() => {
const element = document.createElement('div');
document.body.appendChild(element);
vm.$mount(element);
}, 0)
Besides all the great answers here that say using $mount is better, another thing I would like to add is about the correctness of your code for when it gets evaluated by clean-code-tools (like SonarQube etc).
In short, the code is cleaner when using $mount separately. Because otherwise the clean-code-tools complains:
"Objects should not be created to be dropped immediately without being used"
So in this example the clean-code-tool complains:
new Vue({
el: '#some-id',
...
})
The solution is:
let instance = new Vue({
...
})
instance.$mount('#some-id')
And so everybody is happy again
I'm a beginner, this is probably more of a javascript problem than vue but anyway:
there a plugin for spreadsheet named handsontable and in the normal use you make the table by doing this
hot = new Handsontable(container, {option})
and then you can use the method like hot.loadData() etc..
To use handsontable with vuejs, there a wrapper we can find here https://github.com/handsontable/vue-handsontable-official. With the wrapper you make a table like this :
<template>
<div id="hot-preview">
<HotTable :root="root" :settings="hotSettings"></HotTable>
</div>
</template>
<script>
import HotTable from 'vue-handsontable-official';
import Vue from 'vue';
export default {
data: function() {
return {
root: 'test-hot',
hotSettings: {
data: [['sample', 'data']],
colHeaders: true
}
};
},
components: {
HotTable
}
mounted () {
localforage.config({
driver: localforage.INDEXEDDB,
name: 'matchlist-database'
})
localforage.getItem('DB').then(function (value) {
console.log('then i fetch the DB: ' + JSON.stringify(value))
if (value !== 'null') {
console.log('dB contain something')
**root**.loadData(value)
}
</script>
So it work fine when i give an array but to load the data from a DB you must call the handsontable method hot.loadData(data).
i cannot find how to call this method in vuejs i always get the error
TypeError: root.loadData is not a function
i tried with all i could think of instead of root ex: HotTable.loadData(value)
but to no avail
Can someone point me out how i would call handsontable methods from the vuejs wrapper. Or point me out what kind of reading i should do to understand my mistake. Thank a lot
There are two problems here, not bad ones :)
1st problem:
If you want to refer to your data inside Vue's methods/computed properties/watchers/lifecycle events, you should use the this keyword. If you have data: function() { return { root: "root-value" }} and you would like to console.log that "root-value" string, you should write console.log(this.root) inside your mounted handler.
If you had something like:
data: function() {
return {
hot = new Handsontable(container, {option})
....
};
You could call hot.loadData() like so:
mounted() {
this.hot.loadData();
...
}
So this refers to the Vue instance which exposes your data properties.
2nd problem:
If I understand the component wrapper correctly, you are supposed to pass data to it as props, not call any Handsontable methods directly.
<HotTable :root="root" :settings="hotSettings"></HotTable>
This means that Vue passes whatever you have as root in your data to the HotTable component. It also passes whatever you have as settings in your data. In the example, HotTable receives these:
root: 'test-hot',
hotSettings: {
data: [['sample', 'data']],
colHeaders: true
}
Now if you want to change/update/modify/add data that should be passed to the HotTable component, you should update your data in the Vue instance. You should do something like this.hotSettings = something new and this.root = something else and the HotTable component would receive those.
To understand what's really happnening with the HotTable, read all of the component documentation. Really. You will save lots of time if you read through the documentation. It all makes sense after that!
https://v2.vuejs.org/v2/guide/components.html
I need to find a way to create dynamic component instances programmatically (instead of through a template).
Although I have found a solution (it seems), the naive way of just create a new vue-instance using new Vue(..) results in an error:
Failed to mount component: template or render function not defined.
This seems strange to me, since it should just be possible to do so afaik. I.e.: there's a template defined on the extended vue class.
Please see the code below, with 2 commented out ways that work, and the current (non commented out) code that doesn't work.
My contrived code:
const HelloComponent = Vue.extend({
template: '<p>Welcome home!</p>'
});
const Home1 = {
template: '<p>Welcome home!</p>'
};
const Home2 = {
extends: HelloComponent
};
new Vue({
el: '#app',
data() {
return {
// currentView: Home1 // does work
// currentView: Home2 // does work
currentView: new HelloComponent() //does NOT work. Why?
};
},
template: '<component :is="currentView"></component>',
});
The built in component component can accept a string, a component constructor, or a component definition object. Vue.extends creates a new component constructor function. To make your code work you should pass the constructor function itself, not the result of creating it.
currentView: HelloComponent
Essentially, the result of new HelloComponent() is not a component definition object or a component constructor function, it's a Vue instance.