Important VueJs Interview Questions

Introduction

New technologies and libraries appear on the web in this growing digital era, indicating that the web is rapidly evolving. Vue.js is a Javascript framework that has exploded in popularity in recent years. So it is essential to go through its questions before appearing for an interview.

In this article, we will learn the important VueJs interview questions. So, without any further ado, let's get started!

Q1) What is vue.js?

Answer: VueJS, like ReactJS, is one of the best frameworks for JavaScript. The user interface layer is designed with VueJS, which is simple to learn for any developer. It can also be used with other libraries and extensions. It is employed in the development of a single-page application.

Must Read Web Developer Interview Questions

Q2) What are the features of vue.js?

Answer: The features of vue.js are as follows:

Animation/Transitions: For a transition/animation effect, VueJS has a built-in transition component that must be wrapped around the element.
Components: Components are a key feature of VueJS that aid in the creation of custom elements that can be reused in HTML.
Data Binding: The data binding feature of VueJS allows us to manipulate or assign values to HTML attributes, change the style, and assign classes using the binding directive v-bind.
Routing: The vue-router is used to navigate between pages.
Templates: HTML-based templates are provided by VueJS to bind the DOM to the Vue instance data. The templates are compiled into Virtual DOM render functions by Vue.
Event Handling: In VueJS, the v-on attribute is added to the DOM elements to allow them to listen to events.

Q3) What do you understand by instance in VUE JS?

Answer: A Vue instance is essentially a ViewModel, as defined by the MVVM pattern; that is why we see the variable name vm throughout the documentation. When we create a Vue instance, we must include an option object with data, template, element to mount on, methods, lifecycle callbacks, etc.

Q4) Explain the vue instance life cycle.

Answer: When a vue instance is first created, it goes through a series of initialization steps.

Set up data observation, compile the template, and create the required data bindings. It will invoke some lifecycle hooks along the way, giving us the ability to run custom logic. The created hook, for example, is called after the instance is created:

new Vue({
data: {
a: 1
},
created: function () {
// `this` points to the vm instance
console.log('a is: ' + this.a)
}
})
// => "a is: 1"

Other hooks will be called at various stages of the instance's lifecycle, such as when it is compiled, ready, or destroyed. All lifecycle hooks are invoked with this context pointing to the Vue instance that invoked them. The concept of "controllers" doesn’t exist. These lifecycle hooks would be used to split your component's custom logic.

Q5) How to create an instance of Vue js.

Answer: The Vue function allows us to make a Vue instance:

var x = new Vue({
// options
})

Q6) Differentiate between two-way data binding and one-way data flow?

Answer: The difference between two-way data binding and one-way data flow is as follows:

Two-way data binding	One-way data flow
When the data model changes in a two-way data binding application, the view(UI) part automatically updates.	The application’s view(UI) part does not update automatically when a data model is changed in a one-way data flow.
For two-way data binding in Vue.js, the v-model directive is used.	Vue js uses v-bind for one-way data flow and binding.

Q7) How to create Two-Way Bindings in Vue.js?

Answer: Using the v-model directive, we can quickly implement two-way binding between form input and the app state. In Vue js, the v-model directive is used to create two-way bindings. In two-way bindings, the data or model is bound to the DOM, and the DOM is then bound to the model.

We can see how two-way bindings are implemented in the example below:

<div id="ninja">
{{message}}
<input v-model="message">
</div>
<script type="text/javascript">
var message = 'Vue.js is rad';
new Vue({ el: '#app', data: { message } });
</script>

Q8) What are filters in Vuejs?

Answer: Filters are a Vue component feature that can be used to apply formatting and transformations to any part of the dynamic data in a template. The component's filter property is an object. Mustache interpolations and v-bind expressions are two places where it's used. The data is primarily filtered at the DOM level. As a result, we get data that is still intact in storage but is represented in the way we specify. It improves the appearance of the view layer. The filters can also be reused. A filter can be declared globally and applied to any desired component. It gives us control over how our data is formatted at the view level.

Q9) How can we create a custom filter in Vue.js?

Answer: In Vue js, the Vue.filter() method is used to create and register a custom filter. The filterId parameter of the Vue.filter() process is a unique name for the filter we will create. The filter function takes a value as an argument and returns the transformed value.

Vue.filter('reverse', function (val) {
return val.split('').reverse().join('')
})

Q10) What are Vue.js components? How can we register one component inside another?

Answer: Vue Components are one of Vue js' most powerful features. Components are Vue instances that can be reused and have custom HTML elements. Components can be reused as many times as desired, or they can be used as a child component in another component.

The method for registering a Vue component inside another component is as follows.

export default {
el: 'element1'
components: {
'element2'
}
}

Q11) In VUE.js, what are directives?

Answer: Vue.js directives allow us to add new attributes and tags to HTML. Vue.js comes with a set of built-in directives that give our apps more functionality. Vue.js can be used to create custom directives. Vue.js directives allow us to add new attributes and tags to HTML. Vue js' directive concept is far more straightforward than Angular.

The following is a list of Vue.js directives that are frequently used.

v-else
v-if
v-model
v-on
v-show

Q12) List the different types of directives available in Vuejs.

Answer: The directives listed below are available in Vue js.

Custom Directives
Empty Directives
General Directives
Literal Directives

Q13) What is VUE-resource and how do we install it?

Answer: VUE-resource is a vue.js plugin that allows us to make web requests and handle responses using an XMLHttpRequest or JSONP.

We can install it using yarn or NPM.
$ yarn add vue-resource
$ npm install vue-resource

Q14) How do we create constants in Vue js?

Answer: The keyword const is used to create a constant. It is recommended to create a separate file for defining constants in Vue.js.

Example:

In Vue js, we can create a constant.

export const SITE_URL:

'https://www.codingninjas.com';

Importing a constant in Vue js:

import {SITE_URL} from

'./path/to/constants.js';

15) What do you mean by virtual dom in Vuejs?

Answer: In Vue, the Document Object Model (DOM) is represented by the Virtual DOM, which is a JavaScript object. Instead of updating the DOM directly, the application updates the Virtual DOM. As a result, it reduces the real DOM's updating cost, which is computationally expensive.

The timing at which the Virtual DOM is rendered can be controlled with Virtual DOM. Until we choose it, Virtual DOM will just keep the data in its current state without re-rendering it. Virtual DOM can also help us to improve the performance of our web apps by reducing the number of times the DOM needs to be updated.

Q16) Why are Vue.js mixins required?

Answer: In Vue JS, a mixin is a chunk of defined logic that is stored in a specific way. It can be reused to add functionality to Vue instances and components.

There are several advantages of mixins that are as follows:

Mixins make it simple to follow the DRY (Don't Repeat Yourself) principle.
Mixins provide a lot of flexibility. Options for Vue components are included in the Mixin.
Mixins are harmless and have no effect on changes that occur outside of their defined scope.
Vue JS's mixins provide a fantastic platform for code reuse.

Q17) What is Vuex?

Answer: Vuex is a Vue application state management library. It serves as the application's single source of truth and centralizes data flow to various components. Passing props in complex applications with many components can be tedious, but Vuex makes this interaction effortless and scalable.

Q18) How do we create a component in Vue js?

Answer: Components are a single, self-contained unit of an interface in Vue JS. They have their own markup, style, and state.

We can define a Vue component in four different ways:

The first is new Vue({ /*options */ }).
The second is Vue.component(‘component-name’, { /* options */ }).
The third option is to make use of local components.
The fourth can be found in .vue files, also known as Single File Components.

The first two methods are the most common ways to use Vue when creating a non-SPA application (Single Page Application). In the Single Page Application, the Single File Components are used.

Q19) How can we import the js file in the Vue component?

Answer: There are two methods for importing a JavaScript library into a Vue component:

The first step is to load a JavaScript library from the computer. We can use the 'import' keyword inside the script tag of our Vue file to import the JavaScript library.

import * as mykey from '../assets/js/mykey.js';

The second option is to include our external JavaScript file in our Vue component's mounted hook.

Q20) How do we use Vue.js to call a rest API?

Answer: To call REST APIs from Vue JS, we can use a variety of HTTP libraries. Axios is one of the most popular libraries. It's easy to use and portable. Execute the following command to include it in the project.

npm install axios --save

Using Axios to implement the GET method in Vue JS:

axios({ method: "GET", "URL": "https://httpbin.org/ip" }).then(result => {
this.ip = result.data.origin;
}, error => {
console.error(error);
});

Using Axios and Promise, we can send an HTTP request. We'll get the result if the request is successful.

Key Takeaways

In this article, we've learned the important interview questions of Vue Js in detail. If you want to learn more about interview questions, you must check here.

If you are curious to learn advanced front-end web development, Coding Ninjas has one of the best courses available, which you can find here.

Recommended Readings:

Thank you for reading!