VueJS Interview Questions and Answers (2024) - Coding

VueJS is a well-liked JavaScript framework. It is utilized for building dynamic user interfaces and single-page applications. It provides component-based architecture and supports two-way data binding, making form handling easy. As VueJS continues to uplift in popularity, it is more and more becoming a usual topic in front-end developer job interviews. We present a complete list of top VueJS interview questions and answers modified for both freshers and experienced developers. To prepare you for interviews, we have compiled the top 50 VueJS questions suitable for freshers, intermediate, and experienced candidates.

Basic VueJS Interview Questions for Freshers

1. What is VueJS?

VueJS is a JavaScript framework used for building user interfaces and dynamic single-page applications. VueJS is mostly concentrated on the view part of the application that is also known as front end development. It is going popular day by day because it is very simple to integrate with other projects and libraries.

2. What is a Single-Page Application?

Single Page Applications (SPAs) load once and robustly update content, reducing wait time for users. It uses JavaScript to fetch data and update the web page without necessitating to reload everything.

3. What is a component in VueJS? How can we create a component?

A component in VueJS is a reusable piece of code that signifies a part of the user interface. Components make it simpler to handle complex applications by splitting them down into minor, controllable pieces.

To make a component in VueJS, pursue these steps:

Create a new component by defining it with ‘template’ , ‘script’ , and ‘style’.

HTML

<template>
  <div>
    <h1>Hello, {{ message }}</h1>
  </div>
</template>

<script>
export default {
  name: 'MyComponent',
  data() {
    return {
      message: 'gfg'
    }
  }
}
</script>

<style scoped>
h1 {
  color: blue;
}
</style>

JavaScript

import MyComponent from './MyComponent.vue'

new Vue({
  el: '#app',
  components: {
    MyComponent
  }
})

Use the component in your template with its custom tag.

HTML

<div id="app">
  <my-component></my-component>
</div>

4. What are Props in VueJS?

Props in VueJS are custom attributes that permit parent components to pass data to child components. They empower component reusability by producing it possible to handle child components from their parent. They are specified in the child component and received as arguments from the parent.

Syntax:

Vue.component('child-component', {
  props: ['propName'],
  // define component
});

5. What is the difference between one-way data binding and two-way data binding in VueJS?

One-way data binding	Two-way data binding
Data flows from model to view.	Data flows both ways between model and view.
It is commonly used with the ‘v-bind’ directive or the ‘ {{ }} ‘ mustache syntax to dynamically update the view whenever the model changes.	It is typically used with form elements and the ‘v-model’ directive.
It follows static binding in the data model.	It follows Dynamic binding in the data model

6. What is a VueJS Router?

Routing in VueJs is used to navigate the Vue application, permitting the formation of single-page applications with multiple views. Vue Router helps link between the browser’s URL/History and Vue’s components empowering for certain paths to render whatever view is linked with it. A Vue router is utilized in making single-page applications.

7. What is a Vue instance? How can we create a Vue instance?

VueJS instance is the root of all Vue application. It is JavaScript object formed by the ‘Vue’ constructor function and assists as the initiating point for building a Vue application.

Creating Vue Instance:

var app = new Vue
({
  // Options object
  el: '#app', // The element to mount the Vue instance to
  data: 
{
    message: 'Hello GeeksForGeeks!'
  }
)}

8. What are Filters in VueJS?

VueJS filter is defined as Vue components that offer features called filters to apply text formatting on any part of the data templates dynamically. They are mainly applied in ‘v-bind’ expressions. Filters can perform tasks like formatting dates, capitalizing text.

Syntax:

{{ message | filterName }}

9. In VueJS, what is the purpose of nextTick?

After the data have been set and the DOM changed, the nextTick method is only easy solution to perform a function.

10. How do you handle errors and exceptions in VueJS applications?

In VueJS, the ‘errorCaptured’ lifecycle hook permits to control errors taking place in a component and its child components. For application-wide error handling, you can apply global error handlers like ‘Vue.config.errorHandler’ .

11. How do you create custom events in VueJS?

In VueJS, custom events are formed applying the ‘$emit’ method within a child component to activate an event. The parent component listens for this event using the ‘v-on’ directive or its shorthand ‘@’ . This grants communication between a child and parent components.

12. Explain Virtual Dom in VueJs?

In VueJS, the Virtual DOM (VDOM) is an approach used to upgrade execution when updating web pages. It works like a blueprint of the real web page’s structure, kept in memory. When a Vue component changes, Vue first update VDOM instead of directly editing the real DOM. Then, it matches the improved VDOM with the earlier one to figure out the smallest number of changes vital in the real DOM. This method lessens the number of upgrades to the existing web page, forming Vue applications rapid and more responsive, notably with often data changes.

13. Explain Hooks in VueJS? what are the different built-in Hooks in VueJS?

Hooks are a new feature introduced in VueJS 3. Hooks are functions that permit adding reusable logic to components. They permit managing state, lifecycle events, and side effects within functional components.

Some of the most typically used hooks include:

‘onMounted’ : The ‘onMounted’ hook enacts directly after the component is mounted onto the DOM. It is best for executing tasks like DOM manipulations or fetching data, assuring these operations happen at the right moment while the component’s lifecycle.
‘onUnmounted’ : The ‘onUnmounted’ hook initiates just before the component is eliminated from the DOM. It is impeccable for doing cleanup tasks, assuring that any vital operations are done before the component is no longer active in the application

14. What is a Key in VueJS?

In VueJS, a “key” is a unique attribute used mainly to discover nodes in a list of components rendered utilizing ‘v-for’ . When Vue renders multiple items with ‘v-for’ , it uses keys to capably update the DOM elements. Using keys correctly helps Vue efficiently update the DOM by reusing extant elements based on changes in data, rather than re-rendering everything from scratch, thus refining execution and stopping unneeded re-renders.

15. Describe the distinction between ‘v-show’ and ‘v-if’ ?

v-show	v-if
Has a higher initial render cost when first displayed, but toggling the visibility is very cheap as it only changes the CSS	Has a higher initial render cost because it involves adding or removing elements from the DOM.
The element is rendered and added to the DOM, but it is hidden if the initial condition is false.	The element is not rendered at all if the first condition is false.
Ideal for scenarios where you need to frequently toggle the visibility of elements without the overhead of adding or removing them from the DOM.	Best suited for scenarios where elements or components are expensive to create or destroy, and the condition changes infrequently.

16. What is the difference between ‘$emit’ and ‘$on’ in VueJS?

‘$emit’	‘$on’
Used to send (emit) custom events from a child component.	Used to listen for (receive) and handle custom events in a parent or ancestor component.
Typically used in a child component to notify a parent component.	Can be used in both parent and child components to handle events.
Sends events upward in the component hierarchy (child to parent).	Can handle events in any direction, depending on where it is used (parent to child or child to parent).

17. Who is the founder/ inventor of VueJS?

Evan You, the creator of VueJS, developed the framework while working at Google on various Angular projects.

18. What is a local component in VueJS?

Local components are defined inside a specific component and are accessible only within that component or its child components.

19. What is a global component in VueJS?

A global component in VueJS is a component that is registered globally, forming it accessible for use in any part of the application. This permits the component to be reused over varied templates without requiring to import it each time.

20. What is the purpose of the ‘data’ function in Vue components?

The ‘data’ function is applied to clarify the reactive data properties for a component. Such data properties are part of the component’s state and can be acquired in the component. The ‘data’ function must return an object that covers the properties you seek to be reactive.

<template>
  <div>
    <p>{{ message }}</p>
    <button @click="updateMessage">Update Message</button>
  </div>
</template>

<script>
export default {
  name: 'ExampleComponent',
  data() {
    return {
      message: 'Hello, GFG'
    }
  },
  methods: {
    updateMessage() {
      this.message = 'Welcom to GFG'
    }
  }
}
</script>

21. What is Vue CLI and how is it used?

Vue CLI (Command Line Interface) is a tool for fast support VueJS projects. This is a command-line utility that permits you to choose from a range of build tools. With Vue CLI, developers can rapidly set up a new project with best practices and modern build tools like Webpack or Vite.

Intermediate VueJS Interview Questions

22. How do you pass data between components in VueJS?

Here are the usual ways to pass data between components:

Props: Props are used to pass data from a parent component to a child component.

HTML

<!-- App.vue -->
<!-- Parent Component -->
<template>
  <child-component :message="parentMessage"></child-component>
</template>

<script>
import ChildComponent from './ChildComponent.vue';

export default {
  components: {
    ChildComponent
  },
  data() {
    return {
      parentMessage: 'Hello from parent component'
    };
  }
};
</script>

HTML

<!-- childcomponent.vue -->
<!-- Child Component -->
<template>
  <div>{{ message }}</div>
</template>

<script>
export default {
  props: {
    message: String
  }
};
</script>

Event Bus: An event bus can be used to enable communication between sibling components.

JavaScript

// EventBus.js
import Vue from 'vue';
export const EventBus = new Vue();

JavaScript

// Component1.vue
<template>
  <button @click="sendData">Send Data</button>
</template>

<script>
import { EventBus } from './EventBus';

export default {
  methods: {
    sendData() {
      EventBus.$emit('data-sent', 'Hello from sibling component 1');
    }
  }
};
</script>

JavaScript

// Component2.vue
<template>
  <div>{{ receivedData }}</div>
</template>

<script>
import { EventBus } from './EventBus';

export default {
  data() {
    return {
      receivedData: ''
    };
  },
  created() {
    EventBus.$on('data-sent', (data) => {
      this.receivedData = data;
    });
  }
};
</script>

23. What are slots in VueJS?

Slots are placeholders in a component’s template that permit content to be passed into them from the parent component. They empower the formation of reusable components by giving a way to insert components into predefined slots. It can be named or unnamed (‘default’), allowing versatility in how content is divided. This attribute is notably valuable for forming components that need dynamic layouts, where the structure might vary depending on where the component is used.

24. How do you handle asynchronous operations in VueJS?

Asynchronous operations are usually controlled using promises or async/await syntax. Promises permit chaining of .then() and .catch() to handle asynchronous responses from APIs. Instead, async/await gives a cleaner syntax by permitting asynchronous functions to be written in a synchronous style.

25. What is the watcher in VueJS?

A watcher is a mechanism designed to notice modifications in data properties in a component. It permits to respond to these modifications by enacting defined functions.

Syntax:

export default {
  data() {
    return {
      message: 'Hello GFG'
    };
  },
  watch: {
    message(newValue, oldValue) {
      console.log(`Message changed from ${oldValue} to ${newValue}`);
      // Perform actions based on the change
    }
  }
}

26. What is Vue-loader?

Vue Loader is a webpack loader for VueJS that permits to write Vue components in ‘.vue’ file format. It empowers VueJS applications to use Single File Components (SFCs), which encapsulate HTML, CSS, and JavaScript into a single file. They compile these components into JavaScript modules that the browser can grasp, easing component-based development in VueJS projects.

27. What are the different types of directives present in VueJS?

Vue directives, marked by the prefix v- . These directives form a perfect connection to the Vue instance, facilitating the formation of a responsive user interfaces that react to changes in data and user interactions.

Here are the major kinds of directives in VueJS:

v-bind
v-model
v-for
v-on (or @)

28. What is server-side rendering (SSR) in VueJS?

Server-side rendering in VueJS includes rendering Vue components on the server before sending HTML to the client. This boosts first page load execution by delivering pre-rendered content.

29. Explain features of VueJS?

Here are some of the features of VueJS:

VueJS permits building applications using components, which encapsulate both data and UI elements into reusable blocks.
VueJS gives built-in transition system that can apply CSS transitions and animations when elements are inserted, updated, or removed from the DOM.
VueJS supports server-side rendering to boost SEO and initial load times of applications.

30. How Do You Bind Class and Style in VueJS?

To robustly bind classes and styles in VueJS, use the ‘v-bind’ directive. You can obtain class binding using any ‘:class’ or ‘v-bind:class’ .

<div :class="{ active: isActive, 'text-danger': hasError }"></div>

Use the :style or v-bind:style directive to use inline styles dynamically.

<div :style="{ color: activeColor, fontSize: fontSize + 'px' }"></div>

31. How do you optimize the performance of a VueJS application?

To optimize VueJS applications, fixate on lowering excessive re-renders using memoization.

Use Vue’s virtual DOM for competent updates, and enhance components with ‘v-if’ , ‘key’ attributes in ‘v-for’ , and lifecycle hooks like ‘shouldComponentUpdate’ .
Apply lazy loading with Vue Router.
Apply Vue DevTools for profiling, consider SSR for SEO and first load speed.

32. What Is The Difference Between Functional And Class-based Components?

Functional components in VueJS are stateless, and have no lifecycle hooks, giving performance benefits for easy presentational tasks. Class-based components, on the other hand, are sustaining full Vue features like lifecycle hooks, state management, and more complex logic, adequate for dynamic, interactive components.

33. Explain the Concept Of Higher-order Components in VueJS?

HOCs are functions that take a component and return a new component with boosted features. This pattern is energized by higher-order functions in JavaScript, which are functions that work on other functions.

34. What Are the Best Practices for Component Naming in VueJS?

Here are certain crucial strategies for component naming in VueJS:

Use PascalCase for Component Names: Vue assists ‘PascalCase’ for component names, ‘PascalCase’ is chosen, particularly when using ES6 import statements. An Example: ‘MyComponent.vue’ .
Meaningful Names: Components should be named based on their functionality. An Example: In place of ‘Button.vue’ , use ‘SubmitButton.vue’ if the component particularly manages submit actions.
Avoid Generic Names: Avoid utilizing overly generic names like ‘Button’ , ‘Item’ , or ‘List’ . These names do not express exact operations. An Example: apply ‘UserProfileCard.vue’ in place of just ‘Card.vue’ .

35. What Are Render Functions in VueJS?

Render function returns virtual DOM node, regularly named VNode in the Vue ecosystem, which is an interface that permits Vue to write these objects in your browser DOM. They include all the information necessary to work with Vue.

36. Can we call the REST API from VueJS?

Yes, you can call REST APIs. You can include it in your project by using the following command.

npm install axios --save  
Implementing GET method using Axios in Vue JS  
axios({ method: "GET", "URL": "https://httpbin.org/ip" }).then(result => {  
                this.ip = result.data.origin;  
            }, error => {  
                console.error(error);  
            });

37. Mention some of the array change detection methods in VueJS?

In VueJS, some of the array change detection and mutation methods are:

push()
pop()
shift()
unshift()
sort()
reverse()

38. What is Vuex?

Vuex is a state management pattern and library for VueJS applications. It acts as a central store for all the components in an application. It applies rules to verify that state changes occur in expected way. When merged with the VueJS DevTools extension, it gives extra strong features.

39. In vue router, what are navigation guards?

Vue-navigation router’s guards protect navigations by diverting or cancelling them. The three possible techniques to plug into router navigations are listed below.

Global
Per-route
In-component

40. How do you handle errors and exceptions in VueJS applications?

41. How can you install VueJS in your project?

To install VueJS in your project, you can follow these steps:

Using CDN: Include VueJS directly via a CDN link in your HTML file:

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/vue.min.js"></script>

Using npm: Install VueJS via npm (Node Package Manager) for more advanced projects:

npm install vue

Vue CLI Create Project: Create a new Vue project using Vue CLI:

vue create my-vue-app
cd my-vue-app
npm run serve

Advanced VueJS Interview Questions for Experienced

42. Why is it recommended not to use v-if and v-for directives together on the same element in VueJS?

It is normally not suggested to use ‘v-if’ and ‘v-for’ directives unitedly on the similar element in VueJS due to potential operation outcomes. Here is why:

Rendering Overhead: When ‘v-for’ iterates over a list, VueJS forms a DOM element for each item in the list. If you merge ‘v-if’ on the same element, VueJS requisites to analyze the ‘v-if’ directive for each iteration to choose whether to render that element. This can lead to unneeded calculations and DOM manipulations.
Readability: Uniting ‘v-if’ and ‘v-for’ can make the template tougher to read and understand, particularly for developers who are new to the codebase. It can unclear the meant logic of rendering elements based on terms.

43. Give an example to demonstrate how can you use event handlers in VueJS?

In VueJS, event handlers are methods that are invoked in response to precise events initiated by user interactions. These events can comprise things like clicks, key presses, mouse movements, form submissions, and more. They are defined within the Vue instance and are normally stated in the methods object.

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
  <title>gfg</title>
  <script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/vue.js"></script>
</head>
<body>
<div id="app">
  <button @click="handleClick">Click me!</button>
  <p v-if="clicked">Button was clicked!</p>
</div>

<script>
  new Vue({
    el: '#app',
    data: {
      clicked: false
    },
    methods: {
      handleClick() {
        this.clicked = true;
      }
    }
  });
</script>
</body>
</html>

44. Name some websites which are using VueJS?

Netflix
Adobe
Facebook
Gitlab
Xiaomi
Alibaba

45. Can You Explain the Single File Components in VueJS?

Single File Components in VueJS conclude a component’s template, logic, and styles in a single ‘ .vue ‘ file. They boost modularity by arranging all features of a component in one place, refining readability. During build, tools like webpack process these files, allowing innovative features like hot-reloading. This way refines VueJS development by supporting component-based architecture.

46. What is $parent property in VueJS?

In VueJS, the ‘ $parent ‘ property gives direct access for a child component to its direct parent component in a nested structure. This permits the child to interact with and use methods.

47. What is vue plugin?

Developers can form and add global level features to Vue via Vue plugin. This can be utilized to add globally available methods to an application. VueFire, Vue plugin that adds Firebase specific methods and binding to the intact application, is an example of Vue plugin.

48. Discuss the v-cloak directive in VueJS?

The ‘v-cloak’ directive in VueJS hides components until they are compiled, preventing the display of compiled Vue templates on page load. It assures an effortless user experience by excluding the wavering outcome generated by delayed rendering, utilizing CSS to hide elements as far as Vue processing completes.

49. List out some of the event modifiers in VueJS?

In VueJS, event modifiers are directives that can be affixed to the v-on directive to change how events are controlled. Some usually used event modifiers contain:

.stop: Stops event propagation.
.prevent: Prevents the default event behavior.
.capture: Adds an event listener in capture mode.
.passive: Boosts scrolling performance.

50. What are some popular testing frameworks for VueJS?

Some popular testing frameworks for VueJS comprises:

Jest
Mocha
Cypress
Karma

Reffered: https://www.geeksforgeeks.org

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