Error in Vue.js: the variable has not been defined

Upon stumbling upon this Codepen showcasing a personality quiz designed for an HTML file with a Vue instance, I took it upon myself to transform it into a Vue.js file. However, despite making some minor modifications to align it with Vue.js standards, I encountered the following error message:

   45:17  error  'quiz' is assigned a value but never used  no-unused-vars
  139:19  error  'quiz' is not defined                      no-undef

I recall reading similar queries regarding variables being assigned but left unused, so I added a console.log(quiz.title) line which seemingly resolved the initial error (although I'm unsure if this is the optimal solution). Yet, the second error relating to 'quiz' remaining undefined continues to puzzle me. What could be causing this issue?

<template>
    <div id="app" v-cloak>
        <div class="row">
            <div class="large-12 columns">
                <h1>{{ quiz.title }}</h1>
                <div class="callout">
                    <div v-for="(question, index) in quiz.questions" v-bind:key="question.id">
                        <div v-show="index === questionIndex">
                            <h3>{{ question.text }}</h3>
                            <ol>
                                <li v-for="response in question.responses" v-bind:key="response.id">
                                    <label>
                                        <input type="radio" v-bind:value="response.value" v-bind:name="index" v-model="userResponses[index]">{{response.text}}
                                    </label>
                                </li>

                            </ol>
                            <button class="secondary button" v-if="questionIndex > 0" v-on:click="prev">prev</button>
                            <button class="success button" v-on:click="next">next</button>
                        </div>
                    </div>
                <div v-show="questionIndex === quiz.questions.length">
                    <h3>Your Results</h3>
                    <p>You are: {{ score() }}</p>
                </div>

            </div>

        </div>
    </div>
</div>
</template>

<script>

export default {
  name: 'PersonalityTest',
  components: {
  },
    created() {
        window.addEventListener("load", this.onWindowLoad);
    },
    methods: {
        onWindowLoad() {
            let quiz = {
            title: 'What superhero are you?',

            questions: [{
                id: 1,
                text: "How would you describe your personality?",
                responses: [{
                        text: 'Im serious and dark',
                        value: 'Batman'
                    },
                    {
                        text: 'Arrogant, but charming',
                        value: 'Superman'
                    },
                    {
                        text: 'Fun and easy going',
                        value: 'The Flash'
                    }
                ]
            },
            {
                id: 2,
                text: "Why did you want to become a superhero?",
                responses: [{
                        text: 'For the thrills',
                        value: 'The Flash'
                    },
                    {
                        text: 'For justice',
                        value: 'Batman'
                    },
                    {
                        text: 'For popularity',
                        value: 'Superman'
                    }
                ]
            },
            {
                id: 3,
                text: "Who would you most hang around with?",
                responses: [{
                        text: 'Wonder Woman',
                        value: 'Superman'
                    },
                    {
                        text: 'Green Arrow',
                        value: 'The Flash'
                    },
                    {
                        text: 'Robin',
                        value: 'Batman'
                    }
                ]
            },
            {
                id: 4,
                text: "What's your favourite colour?",
                responses: [{
                        text: 'Black',
                        value: 'Batman'
                    },
                    {
                        text: 'Red',
                        value: 'The Flash'
                    },
                    {
                        text: 'Blue',
                        value: 'Superman'
                    }
                ]
            },
            {
                id: 5,
                text: "When do you help people?",
                responses: [{
                        text: 'Every chance I can',
                        value: 'The Flash'
                    },
                    {
                        text: 'At night',
                        value: 'Batman'
                    },
                    {
                        text: 'When they need me to',
                        value: 'Superman'
                    }
                ]
            },
        ]
    };
    console.log(quiz.title)
    },

    data() {
        return{
            quiz: quiz,
            questionIndex: 0,
            userResponses: Array()
        }
    },
    methods: {
        // Go to next question
        next() {
            this.questionIndex++;
            console.log(this.userResponses);
        },
        // Go to previous question
        prev() {
            this.questionIndex--;
        },
        score() {
            //find the highest occurrence in responses
            var modeMap = {};
            var maxEl = this.userResponses[0],
                maxCount = 1;
            for (var i = 0; i < this.userResponses.length; i++) {
                var el = this.userResponses[i];
                if (modeMap[el] == null)
                    modeMap[el] = 1;
                else
                    modeMap[el]++;
                if (modeMap[el] > maxCount) {
                    maxEl = el;
                    maxCount = modeMap[el];
                }
            }
            return maxEl;
        }
        }
    },
}

</script>
javascriptvue.js

Answer №1

The main issues lie in the way the variable quiz is defined within the function onWindowLoad() { but never utilized outside of it, limiting its scope.

Furthermore, in the data section, there is an attempt to access quiz which has not been properly defined.

There are several potential solutions ranging from less ideal to more optimal approaches:

Solution One

Incorporate the assignment of this.quiz within onWindowLoad(), and declare quiz:{} in the data section.

export default {
    name: 'PersonalityTest',
    components: {},
    create() {
        window.addEventListener("load", this.onWindowLoad);
    },
    methods: {
        onWindowLoad() {
            this.quiz = {
                title: 'What superhero are you?',
                questions: [ ....]
            };
        },

        data: function () {
            return {
                quiz: {},
                questionIndex: 0,
                userResponses: Array()
            }
        },
    },
    ....
}

Solution Two

Rather than using onWindowLoad(), directly define quiz within the data section for clarity.

export default {
    name: 'PersonalityTest',
     components: {},
      data: function () {
          return {
              quiz: {
                title: 'What superhero are you?',
                  questions: [ ....]
              },
              questionIndex: 0,
              userResponses: Array()
          }
      },
      ....
}

Solution Three

Alternatively, consider storing the quiz data in an external file for better organization.

import quiz from "./quiz.js";

 export default {
    name: 'PersonalityTest',
     components: {},
      data: function () {
          return {
               quiz: quiz,
               questionIndex: 0,
              userResponses: Array()
           }
       },
       ....
}

Contents of quiz.js:

export default {
    title: 'What superhero are you?',
    questions: [ ....]
};

Solution Four

Depending on your development environment, importing a JSON file like quiz.json might be a feasible option as well.

import quiz from "./quiz.json";

where quiz.json contains:

{
    title: 'What superhero are you?',
    questions: [ ....]
}

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