If anyone should encounter the same trivial issue I faced, always double-check that the 'data' property in your component is spelled correctly. (for example, data, not date)

<template>
  <span>{{name}}</span>
</template>

<script>
export default {
name: "MyComponent",
data() {
  return {
    name: ""
  };
}
</script>

The issue I encountered was simply due to my forgetting to include the closing tag:

</script>

However, this oversight resulted in the same error message being displayed.

If you encounter this issue, be sure to verify that you do not have

methods: {
...
}

or

computed: {
...
}

stated twice

Don't Forget to Give Back the Item

One common reason for encountering the error message Property "search" was accessed during render but is not defined on instance is when you overlook returning the variable in the setup(){} function

Therefore, always include the return statement at the end:

export default {

  setup(){

    const search = ref('')
    //Any other code

    return {search}

  }
}

Please note that I am utilizing the Composition API

This issue is most likely due to a spelling mistake

I accidentally made a typo in the closing tag of the script

</sscript>

Just wanted to add a quick note for anyone facing similar issues like I did - remember that methods is a case-sensitive term:

<template>
    <span>{{name}}</span>
</template>

<script>
export default {
  name: "MyComponent",
  Methods: {
      name() {return '';}
  }
</script>

Make sure to use 'methods' instead of 'Methods'

When you have two instances of Vue in your code, you may encounter an error. For instance, if you have one in your app.js file and another in a custom script tag in your view file, it's best to stick to just one instance.

 const myVueApp = new Vue({
    el: '#app',
});

During my attempt to assign a component property to a state property while instantiating, I encountered this error message

export default {
 props: ['value1'],
 data() {
  return {
   value2: this.value1 // triggers the error
   }
  }, 
 created(){
  this.value2 = this.value1 // resolves the issue
 }
}

I encountered a problem when I mistakenly placed my methods inside the data object. To resolve this issue, simply structure it like the following for optimal functioning.

<script>
module.exports = {
    data: () => {
        return {
            name: ""
        }
    },
    methods: {
        myFunc() {
            // code
        }
    }
}
</script>

For me, I mistakenly typed "method" instead of "methods". What a silly mistake. It ended up costing me almost an hour of wasted time.

Common Scenarios Leading to This Issue

• Ensure that the 'data' property within your component is spelled correctly
• Make sure that your template is not nested within another component's template
• Verify that the variable is defined inside the data object
• Ensure that your router name is declared as a string

Find more solutions here

One common mistake that can occur when working with Vue.js is mispelling reserved Vue.js variables. In my case, I encountered an issue because I mistakenly misspelled computed:, causing Vue.js to not recognize my computed property variables. Always double check your spelling to avoid similar errors!

I had a pair of solutions: within the <script> section, which just proves that sometimes the answer to a problem can be right in front of you all along.

When working with the Vue3 <script setup> style, be sure to include setup in the opening script tag:

<script setup>

It's easy to slip back into old habits and only use <script> without realizing the mistake right away.

For more information, visit https://v3.vuejs.org/api/sfc-script-setup.html

Ensure that all props and imported variables are correctly set up by using the following method:

Be sure to initialize those variables:

import { item1, item2} from './constants'

//or

export default {
     data(){
      return {
       item1: 0,
       item2: 0,
       item3: 0,
      },
    },
    props: ['item3'],
    created(){
     this.item1 = item1;
     this.item2 = item2;
     this.item3 = item3;
     }
    

I encountered a situation where a property was causing an error, even after correcting the code. After trying various solutions without success, I decided to press Ctrl + F5 and magically the error disappeared! Success! :)

Pay close attention to this warning: Property _____ was accessed during render but is not defined on instance. To resolve this issue, make sure to define the property in the data function, where variables are commonly initialized in a Vuejs application. I encountered this issue myself and solving it in this way fixed the problem. That's all folks!

Upon review, I realized that I had overlooked including the return keyword:

computed: {
    image(){
        this.productVariants[this.selectedVariant].image;
    },
    inStock(){
       this.productVariants[this.selectedVariant].quantity;
    }
}

To correct this, I made the following adjustments:

computed: {
    image(){
        return this.productVariants[this.selectedVariant].image;
    },
    inStock(){
       return this.productVariants[this.selectedVariant].quantity;
    }
}

My issue revolved around the organization of my methods. Instead of placing the closing curly brace } after my method functions, I mistakenly placed it before them. This resulted in some functions being left out of the methods function because they were outside of the curly braces. My incorrect structure looked something like this: methods:

{ function , function }, function, function

My situation was caused by the router name not being within a string:

:to="{name: route-name, params: {id:data.id}}"

I resolved it by placing the router name within a string:

:to="{name: 'router-name', params: {id:data.id}}"

I encountered an issue where I needed to send a predefined text value to another component using the following syntax:

 ChildComponent(:displayMode="formMode")

However, the correct approach should have been:

ChildComponent(:displayMode="'formMode'")

It is important to use single quotes to specify the text value instead of referencing a local variable within the component.

Although many answers provided valuable insights, none were able to resolve the issue I encountered, which closely resembled the error message posted by the original poster.

The error was critical as, despite successful rendering of components with data fetched from an API, certain components failed to render when the application was deployed on Firebase hosting.

To address this issue, I made changes in the Parent component responsible for fetching and passing data to child components:

// In this lifecycle hook, I fetched the data and saved it to the store
created() {
  FetchData.getProfile()
    .then(myProfile => {
      const mp = myProfile.data;
      console.log(mp)
      this.$store.dispatch('dispatchMyProfile', mp)
      this.propsToPass = mp;
    })
    .catch(error => {
      console.log('An error occurred:', error.response)
    })
}
// Accessed the store in this section
computed: {
    menu() {
        return this.$store.state['myProfile'].profile
    }
},

// Then, in the template, I passed the "menu" method to the child component
 <LeftPanel :data="menu" />

This resolved the error. Upon redeployment to Firebase hosting, the application worked flawlessly!

I hope this explanation proves helpful to you.

There are various instances that could lead to the occurrence of this error. Let me share an example that I recently managed to fix.

I had initially declared the variable actionRequiredCount in the data section, but I overlooked the fact that I didn't capitalize the letter C in Count when passing the variable as a parameter to a component.

Here is the correct variable:

data: () => {
     return{
       actionRequiredCount: ''
     }
}

In my template, the mistake was present (note the lowercase c in "count"):

  <MyCustomModule :actionRequiredCount="actionRequiredcount"/>

I hope this explanation proves useful to someone facing a similar issue.

Many individuals commonly encounter errors at this point due to:

• a typo or an oversight in declaration/usage
• repeating the mistake in multiple instances

To prevent typos, it is advisable to utilize Vue VSCode Snippets instead of manual typing. This way, you can employ vbase, vdata, vmethod to automatically generate those components for you.
You can also find similar snippets for Vue3 here.
Alternatively, you have the option to create your custom snippets by following these guidelines.

Ensure that you accurately reference all components as detailed here, including:

• data
• props
• computed
• methods
• watch
• emits
• expose

For the second issue, a recommended approach is to search for the specific keyword in your codebase. For instance, use cmd + f + changeSetting in the scenario to check if there is a missing declaration in data, methods, or similar sections.

Alternatively, implementing an ESlint configuration can provide warnings for any codebase issues. Learn how to set up ESlint + Prettier for a Nuxt project effectively here, ensuring efficient code practices with speedy formatting!

Another scenario that often occurs is:

• You have a component (child) extending another component (parent)
• There is a property or method xyz defined under methods or computed on the parent component.
• You are attempting to use the parent's xyz, but the child component has its own methods or computed

Code snippet demonstrating the issue

// 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 situation, you will need to redefine your xyz computed property under computed

Solution 1:

Redefine xyz and include the code from the parent component

// CHILD COMPONENT
export default {
  extends: myParentComponent,
  computed() {
    xyz() {
      // implement something cool!
    },
    childProprty1() {},
    childProprty2() {}
  }
}

Solution 2

Redefine xyz property by reusing code from the parent component (no code duplication)

// CHILD COMPONENT
export default {
  extends: myParentComponent,
  computed() {
    xyz() {
      return this.$parent.$options.computed.xyz
    },
    childProprty1() {},
    childProprty2() {}
  }
}

The reason for my issue was a simple typo where I mistakenly wrote method: instead of methods: (plural). It's a common mistake that can easily happen!

Another item should be included in the lineup.

TLDR: Double-check that you are editing the right file to avoid errors.

Scenario: I found myself grappling with an error in a codebase inherited from a previous company. The issue persisted until I realized there were two files with similar names: search-bar.js and search-bar.vue.js. Both files contained Vue code, but moving my code to the correct file resolved the problem. It may seem trivial, but it's a reminder to be mindful of file names.