I receive an error when I load the page
My code looks like this :
<script>
methods: {
getPicture() {
var base = this;
axios
.get("http://localhost:3000/pictures/" + this.username)
.then(function (response) {
const { pictureData } = response.data;
base.studentImage = "data:image/jpg; base64," + pictureData;
console.log(base.studentImage);
});
},
}, //END OF METHOD
</script>
I want to display image in My front end. Where do I make a mistake ? Thank you in advance.
Welcome to Stack Overflow!
Sadly, I can't comment on this for more clarity, so my response has to be an answer.
This error occurs because the DOM and/or Vue Instance and/or Template uses the value "studentImage" before it is made available or defined incorrectly.
I recommend removing the variable "base" because Vue is very picky with its use of "this," so you usually wanna stay away from explicitly assigning "this" to a variable. As commented by Estus Flask below, this even applies to common JS. Check here for more information on referring to the correct "this" in JS.
Honestly, from what I can see with the code you've shared, that's likely the cause of your error. You'll want to define "studentImage" within your data object so Vue is aware of its existence.
Here is an example:
data: () => ({
studentImage: '',
}),
methods: {
getPicture() {
axios
.get("http://localhost:3000/pictures/" + this.username)
.then(function (response) {
const { pictureData } = response.data;
this.studentImage = "data:image/jpg; base64," + pictureData;
console.log(this.studentImage);
});
},
},
If it is not, then you'll want to make sure you're checking for "studentImage" before using it within the instance and or calling the method "getPicture," in the appropriate lifecycle.
I'm answering this assuming you're using the latest version of Vue, version three.
If this helps, please let me know!
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'm trying out VueJS, with the aim of incrementally updating a jQuery project, but I'm having issues with props in a child component passed through data from a parent component.
My parent component is
// parent_component.js
var parentData = {};
var parentComponent = Vue.component('parentComponent', {
data: function() {
return {
parentData: _parentData
}
},
delimiters: ['((', '))']
})
$.ajax({
url: '/someUrl/',
success: function(response) {
_parentData = response
}
My Child component is:
// child_component.js
Vue.component('child-component', {
template: '<div>((data.someProp))</div>'
props: ['data'],
delimiters: ['((', '))']
})
My HTML is:
// index.html
<parent-component inline-template>
<child-component v-bind:data="parentData"></child-component>
</parent-component>
This all works fine when I update _parentData right after initializing the childComponent. But I actually need to do an Ajax call and update the _parentData, it is not updated in the childComponent.
Nb. I checked that the _parentData object is there in the callback of the Ajax call.
Also, I tried putting the Ajax call in the created option of the childComponent, but this didn't help.
What am I missing?
Update
I guess I made the classic beginner's mistake! As stated here, Vue cannot detect property addition. So I need to define the someProp property on the _parentData before making the async call.
So if I define var parentData = { someProp: '' }; it will work.
See this fiddle: https://jsfiddle.net/maaikeb/anr1e88n/
If you share the AJAX part of code, maybe I can help better, but IMHO I think that the easiest way is emiting a event from children, and catch it with the parent element when the AJAX call is done (success or error).
Events provide a way to inform your parent components of changes in children.
Template Usage:
<my-component v-on:myEvent="parentHandler"></my-component>
<!-- Or more succinctly, -->
<my-component #myEvent="parentHandler"></my-component>
Firing an Event:
...
export default {
methods: {
fireEvent() {
this.$emit('myEvent', eventValueOne, eventValueTwo);
}
}
}
Additionally, you can create global event buses to pass events anywhere in your app
Extracted from here.
Edit
Ok, I didn't understand you well, if you have problems sending data down from parent to children when updating the parent the proper way is the double data binding.
Maybe your problem is that the data is only evaluated in component creation, and your child will be created with the initial value of the parent component...
You can try some different things to solve this, like:
1 - Maybe your issue is related to a change detection caveat
Maybe you're creating a new property in an object...
_parentData = response
...when you should do...
_parentData.$set('someObject.someProperty', someValue)
2 - Use watch on parent instead of created:
watch:{
yourData() {
$.ajax({
url: '/someUrl/',
content_type: 'application/json',
data_type: 'json',
success: function(response) {
_parentData = response
}
})
},
3 - Try using .sync ( deprecated in 2.0 ):
<component :something.sync="variable"></component>
4 - Bind .this to the anonymous AJAX call or use arrow functions as #Bert commented:
success: () => (response) {
_parentData = response
}
Hope it helps!
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