Vue.js Interview Questions

Vue.js is a JavaScript framework frequently preferred by developers. It is used to develop end-to-end user interfaces and a wide range of single-page web applications.

The demand for Vue.js developers is increasing day by day. Before participating in a technical interview, you can familiarize yourself with Vue.js concepts by reading the most frequently asked Vue.js interview questions. Here are some frequently asked Vue.js interview questions. 💼👇

 

Most Popular Vue.js Interview Questions

1. What is Vue.js?

Vue.js is a JavaScript framework used to create user interfaces and single-page applications. It was created in 2014 by Evan You as an alternative to frameworks like AngularJS and React.

Vue.js is inspired by the MVVM (Model - View - ViewModel) Pattern and uses it to create high-quality single-page applications. The core library of Vue.js focuses solely on the view layer and is designed to be adapted incrementally for projects.

Vue.js operates on a single syntax and has a simple design. Vue has numerous built-in features. This feature also makes it preferred by developers.

 

2. What is a Single Page Application?

A Single Page Application (SPA) is a single page where much of the information remains the same and only a few parts need to be updated at a time. For example, when you check your email, you might notice that not much changes during navigation. As you browse your inbox, the sidebar and headers remain the same.

SPA sends only what is needed on each click and the browser processes this information. This is different from traditional page loads where the server recreates and sends the entire page on every click.

This client-side approach makes loading times much faster for users. It also reduces the amount of data that the server needs to send, making the entire process much more cost-effective.

 

3. What is a Vue Instance?

✅ A Vue instance is an example of a Vue class that represents the ViewModel in the Model-View-ViewModel (MVVM) architecture.

✅ A Vue instance is responsible for creating and managing the component hierarchy, managing data and state, and handling the lifecycle.

A basic Vue instance 👇:

• Specifies the DOM element the Vue instance should be mounted to.
• data: Specifies the data object containing the application's state.

 

4. What is a component in Vue.js?

An important feature of Vue.js is the ability to use components. Components are reusable Vue instances with custom elements.

Vue.js components encapsulate the template, style, and behavior of a specific feature or UI element in the application. A component can be composed of other components and can communicate with other components through events.

⬇️ To create components in Vue.js, the 'Vue.component()' method can be used.

 

5. What are props and accessors in Vue?

👉 Props are one of the most fundamental ways of passing data between components in Vue.js.

👉 Accessors are custom attributes that can be registered on a component. They are used to pass data from a parent component to child components.

 

6. What are plugins in Vue?

Plugins are independent codes that add application-level functionality to Vue.js. Plugins provide code reusability. A plugin can be defined as an object or a function.

📍 Vue.js Plugin syntax:

 

7. What is the Mixins feature in Vue.js? How is it used?

Mixins, are concepts that facilitate code reuse in Vue components that perform the same action. Some actions can be defined in mixins and used wherever needed.

Mixins enable code reusability. When a component uses a mixin, it inherits all the properties and methods defined in the mixin.

 

There are two types of mixins in Vue: 

1️⃣ Local Mixins – Local mixins only work when we use the mixin object within a Vue component.

 

2️⃣ Global Mixins - They are used when the same functionality is needed for all components in Vue. Global mixins affect every Vue component.

To create a mixin, you can use the Vue.mixin() function.

 

8. What are the advantages and disadvantages of Vue.js Mixins?

 

9. What is Virtual DOM in Vue.js?

Document Object Model, also known as DOM, is a type of interface that behaves like nodes tied to all markup languages. DOM allows writing over elements, changing styles, and even modifying elements themselves.

Virtual DOM (VDOM) in Vue.js is an in-memory representation of the real Document Object Model (DOM) of a web page. When a Vue.js component is created or updated, a VDOM representation of its current state is created. This is then compared with the previous VDOM representation to determine the minimal set of changes needed to update the real DOM to reflect the updated state. This provides significant performance improvements, especially in large and complex applications.

 

10. What is a lifecycle hook in Vue.js?

🌀 Lifecycle hooks are predefined methods that are triggered when a Vue component is created, updated, or destroyed. These hooks help run code at different stages of the application's lifecycle.

There are eight lifecycle hooks in Vue.js:

1️⃣ beforeCreate: It is the first lifecycle hook called in Vue.js. It is used to initialize data.

 

2️⃣ created: Called after the component is created. It is used for initial setup tasks such as fetching data from an API.

 

3️⃣ beforeMount: Called before the component is mounted to the DOM. It is used to perform necessary DOM manipulations before processing the component.

 

4️⃣ mounted: Triggered when the component is mounted to the real DOM. It is used to perform necessary DOM manipulations after the component has been created.

 

5️⃣ beforeUpdate: Called before the component is updated, to perform pre-update tasks.

 

6️⃣ updated: Called after the component has been updated. It is used to perform necessary post-update tasks.

 

7️⃣ beforeDestroy: Called just before the Vue instance is destroyed and the component is removed from the DOM.

 

8️⃣ destroyed: It is the final stage where the entire Vue instance is destroyed.

 

11. What is Data Binding in Vue.js?

In Vue.js, data binding is the process of binding the content or properties of elements in the user interface (HTML elements) to the data in a Vue component. It helps synchronize data between the Vue instance and the DOM.

It allows us to establish a connection between data and the UI, so any changes made to the data are automatically reflected in the UI and vice versa.

 

1️⃣ Two-Way Data Binding: Data can be updated both within the component and in the user interface.

2️⃣ One-Way Data Binding: Data is only updated within the component and reflected in the UI. Changes made in the UI do not affect the component's data.

 

12. What is Vuex in Vue?

Vuex is a model and library that provides state management for Vue.js applications. It allows defining a centralized store to manage the application's state and provides a way to access and mutate the state from different components.

 

Vuex includes the following core components:

1️⃣ State: It is a centralized object that contains the application's data.

2️⃣ Mutations: Functions used to change the state.

3️⃣ Actions: Used to manage asynchronous operations and trigger mutations.

4️⃣ Getters: Allows for creating new data by processing the state.

5️⃣ Modules: Enables dividing the state into smaller and manageable parts in large-scale applications.

 

13. What is a filter in Vue.js? 

Filters in Vue.js are functions that can be used to transform data in templates. Filters in Vue.js do not directly modify the wherever the data is stored, but only apply formatting to the data.

📍 Filters can be added to a Vue.js application using the Vue.filter()' method and can then be used in template expressions using the '|'. 

 

14. What are the 'v-if' and 'v-show' directives in Vue.js?

'v-if' and 'v-show' are directives that allow conditional rendering of elements in the user interface. 

👉 v-if, is used to conditionally render a block. The block is only rendered if the directive's expression returns a truthy value.

 

👉v-show is a directive used to conditionally display an element.

 

15. What are the differences between v-if and v-show directives?

• ​🆚 In v-if, elements are not included in the DOM. In v-show, elements are included in the DOM but are hidden.
• 16. What is a template in Vue.js?

  Templates are HTML snippets that define the structure and layout of a component in a Vue.js application. They are referred to as the HTML part of the Vue application. 

  They are very similar to standard HTML code, but they include Vue-specific and directives. They allow data to be bound to the user interface and user input to be handled.

  

  
   

  17. What are routers in Vue.js?

  Vue routers are libraries that help establish connections between the browser's URL/history and Vue's components. 

  Routing allows users to navigate between different pages or views within a single-page application without waiting for the application to reload. This makes it feel like using a mobile/desktop application without reloading the entire page. Since the entire page is not reloaded, it also improves performance.

  Vue routers can be used with the following command 👇.

  

  
   

  18. What is $emit in Vue.js?

  In Vue.js, $emit is a method used to trigger an event from within a parent component and perform an action in the parent components or higher up in the hierarchy that listens to this event. In other words, it is used to pass events from child components to parent components.

  
   

  19. What are the directives in Vue.js?

  • ✅ v-for: Used to loop over arrays or objects and render a template for each item.
  • Used to dynamically bind data to an element's attributes, properties, or styles.
  • Used to add event listeners to DOM elements and call methods when events are triggered.
  • Used to create two-way data bindings.

  
   

  20. How to integrate a third-party library into a Vue.js application?

  To integrate a third-party library into a Vue.js application, the following steps can be taken:

  1️⃣ Install the library: The first step is to add the third-party library you want to use to your project using package managers like npm or yarn. add them to your project using package managers.

  2️⃣ Import the library: You need to import the library so that you can use its components or functions in your Vue component or file.

  3️⃣ Use the library: Before you start using the library, you need to configure or initialize it.