09/June/2021 | 20 minutes to read
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Here is a List of essential Vue.js Interview Questions and Answers for Freshers and mid level of Experienced Professionals. All answers for these Vue.js questions are explained in a simple and easiest way. These basic, advanced and latest Vue.js questions will help you to clear your next Job interview.
These interview questions are targeted for Vue.js that's a JavaScript based framework and used to implement SPAs. You must know the answers of these frequently asked Vue.js interview questions to clear an interview.
1. What is Vue.js?
Vue.js is a JavaScript based framework that is developed to build user interfaces. It's Progressive framework. Vue.js is mainly responsible for view layer only and is easy to integrate with other libraries on existing applications. Vue.js has the capability to develop single page applications (SPA).
2. What are the benefits of using Vue.js over other front end frameworks?
Vue.js comes with many benefits as below.
3. Explain the one-way and two-way data binding.
Vue.js supports both one-way and two-way data binding options.
One-way Binding - It's the most basic form of data binding, you can update classes, styles from JavaScript properties as below.
<span v-bind:class="{ active: isActive }"></span>
<input v-model="message" placeholder="edit me"><span>Message is: {{ message }}</span>
4. How will you create an instance in Vue.js?
Vue's design is partially inspired by the MVVM pattern. That is the reason it's instance is sometimes referred to as 'vm'. You can start the execution of Vue.js application by creating it's instance as below.
var vm = new Vue({
// options
})
5. Explain Interpolations and Binding Expressions in Vue.js.
Both are used for binding.
<span>Message: {{ msg }}</span> // Text binding
<span>{{{ raw_html }}}</span> // use triple Mustache (curly braces) for RAW HTML binding
<span id="item-{{ id }}"></span> // attribute binding {{ number + 1 }}
{{ ok ? 'YES' : 'NO' }}6. Explain directives in Vue.js.
Directive is a special code in the markup that informs the library to perform something with that DOM element. Vue.js has some built-in directives like v-bind, v-model etc. You can create custom directives as well.
// Register a global custom directive called `v-focus`
Vue.directive('focus', {
// When the bound element is inserted into the DOM...
inserted: function (el) {
// Focus the applied element
el.focus()
}
})
// To create a local directive components has directives option as below.
directives: {
focus: {
// directive definition
inserted: function (el) {
el.focus()
}
}
}
// directive usage <input v-focus> 7. Explain the components in Vue.js.
Components are the Vue.js instances that can be reused. Component has a name, with that a component can be used as a custom element inside root vue instance.
// component example
Vue.component('button-count', {
data: function () {
return {
count: 0
}
},
template: '<button v-on:click="count++">You clicked me {{ count }} times.</button> '})
// component usage
<div id="components-work"><button-count></button-count></div>
// js code
new Vue({ el: '#components-work' })
8. How to share the data between components in Vue.js application.
Data flow is useful to share the data between components.
9. Describe the slots and scoped slots?
Slots in Vue.js allow to implement a content distribution API, that serves as a distribution outlet for the content. So here content from the parent component will fill the child component placeholder. Example -
// create a component as below
<navigation-link url="/myProfile">
My Profile
</navigation-link>
// navigation-link template code
<a v-bind:href="url" class="nav-link">
<slot></slot>
</a>
//So When your component renders '<slot></slot>' will be replace by 'My Profile' content.
10. Explain the v-bind and v-model.
v-bind is a directive that is used to reactively update an HTML attribute as below.
<a v-bind:href="url"></a> 11. How will you create and run your vue.js application?
You can create and run your vue.js application with below steps.
node -v and npm -v in command prompt. npm install -g @vue/cli
# OR
yarn global add @vue/clivue create my-app // follow some steps mentioned in the terminal.
# OR
vue uinpm run serve12. What is the component Prop?
Component Prop is used to pass the data from parent component to child component. A component can contain as many as props.
Prop is a custom attribute and when a value is passed to attribute then it becomes property on that component instance.
A component Prop forms a One-way down binding from parent to child component. When any change happens to parent property it flows to child but not child to parent.
So when Parent component is updated, all child components will also get updated. So it will allow you not to mutate the prop in the child component.
13. Explain the filters.
Filters are used to format the text in your application. These are used with interpolations and v-bind expressions. Filters can be applied at the end of JavaScript expression followed by the Pipe '|' symbol. Example of filter:
{{ message | makeCapitalize }}
// makeCapitalize is custom filter defined in your component
filters: {
makeCapitalize: function (value) {
if (!value) return ''
value = value.toString()
return value.charAt(0).toUpperCase() + value.slice(1)
}
}
14. Explain the Vue.js mixins.
Mixins in Vue.js provide a flexible way to reuse the functionalities or code to the Vue instances and components. Mixins are written in a separate file
and can be shared across the components over and over.
When a component uses the Mixin then options of mixin become the part of component's options means they are merged with component's options.
You can also create Global Mixins, but use them with caution as it will affect every Vue.js instance created afterwards.
15. What is the One-Way Data Flow in Vue.js?
One-Way Data Flow - All Props work in one direction means data flow works from parent to child. When any change happens in parent property it automatically updates child property but not vice versa. It prevents a child from mutating the parent property state, which can make your application data flow harder to understand.
16. Describe the Vuex?
Vuex acts as a centralized store for all the components in an application and ensures that the state can be mutated in a predictable way. It's a State Management Pattern plus Library for the applications developed in Vue.js.
17. How will you solve common causes of memory leaks in Vue.js applications?
18. Explain the single file component.
Single File components or SFCs are like any other component except that they are self-contained in their own files. SFCs come with the following advantages.
19. What is Reactivity in Vue.js?
Reactivity - Whenever you make any changes in data value then it triggers page update to reflect data changes. Vue data property, computed property are reactive. Services in Vue.js are not reactive. For more you can visit Reactivity in Vue.js
20. Explain the Vue.js lifecycle hooks.
Every Vue instance passes through certain functions called lifecycle hooks. There are 8 lifecycle hooks for each vue.js instance.
21. What is the Key in Vue.js?
Key is a special attribute in Vue that is used as a hint for the virtual DOM algorithm of Vue to differentiate the VNodes when defining a new node
list against an old list.
If the 'key' attribute is not used then Vue uses an algorithm that minimizes element movement and tries to reuse the elements of the same type. But with 'key' attribute elements will be reordered
and the elements without key are destroyed. It's similar to $index in AngularJS. It's mostly used with the 'v-for' directive.
<ul>
<li v-for="item in items" :key="item.id">...</li>
</ul> 22. Explain the difference between v-show and v-if.
v-show and v-if both are used to show or hide the elements. But there are some differences.
23. What is $root in Vue.js?
$root property is used to access the root instance (new Vue()) in every subcomponent of this instance. All subcomponents can access this root instance and can use it as a global storage.
// foo will be available globally
this.$root.foo = 224. Explain the usage of $parent.
$parent is used to access the parent component instance in the child component. It makes the application harder to test and debug and you can not find out where mutation comes from. Similar to $parent Vue also provides a $child that gives a child component instance.
25. Describe the ref in Vue.js.
Vue.js provides the concept of props and events to communicate from parent to child and vice versa. Sometimes you need to directly access child components in JavaScript. To achieve this behavior you can use ref attribute to assign a reference ID to the child component as below.
<base-input ref="usernameInput"></base-input> this.$refs.usernameInput26. How to track the changes in Vue.js?
27. Explain Vue router or how will you implement routing?
28. How will you create constants accessible to the entire application in Vue.js?
29. Explain the Vue.js application Structure.
30. What are the limitations of using Vue.js?
31. How to use local storage in Vue.js application?
32. How to deploy Vue.js app?
33. How to pass arguments to filters?
34. How to listen to component prop changes?
35. How to force Vue.js application to re-render or reload?
36. What is the equivalent of Angular service in Vue.js?
Vue does not provide the concept of singleton service similar to Angular. It encourages you to use Mixin and Store for your shared logic. But you can implement your custom stateful services in Vue.js. For more you can visit this Service in Vue.js.
37. How to bind the styles in Vue.js?
38. How will you toggle a class in Vue.js?
39. What is the difference between a method and computed value?
40. How to communicate between sibling components in Vue.js?
41. How to redirect to another page in Vue.js?
42. How routing works in Vue.js?
43. How to modify global configurations in Vue.js?
To modify global configuration you need to work with Vue.config object. This object contains all global settings. You can change any setting as per your
requirement.
Vue.config.debug = true // to turn on debugging mode
Vue.config.delimiters = ['(%', '%)'] // to set delimiters
44. How to handle the errors in Vue.js?
Error handling is a very important part of any application. Vue.js provides many ways to implement error handling.
Vue.config.errorHandler = function(err, vm, info) {
console.log(`Error: ${err.toString()}\nInfo: ${info}`);
}
err is actual error object, vm is Vue instance and info is error string specified.
Vue.config.warnHandler = function(msg, vm, trace) {
console.log(`Warn: ${msg}\nTrace: ${trace}`);
}
const app = new Vue({
el:'#app',
renderError (h, err) {
return h('pre', { style: { color: 'red' }}, err.stack)
}
})
45. Explain custom events in Vue.js.
46. What is the Jest and Mocha in Vue CLI?
Vue CLI comes with built-in options for unit testing with Jest and Mocha. Jest is a test runner developed by Facebook. It delivers a battery-included solution for unit testing. You can use Vue CLI plugin 'cli-plugin-unit-jest' to
run Jest tests.
Mocha is a JavaScript based test framework that runs on
Node.js and in browsers that makes asynchronous testing easy.
It comes with an integrated webpack precompiler.
1. How much will you rate yourself in Vue.js?
When you attend an interview, Interviewer may ask you to rate yourself in a specific Technology like Vue.js, So It's depend on your knowledge and work experience in Vue.js. The interviewer expects a realistic self-evaluation aligned with your qualifications.
2. What challenges did you face while working on Vue.js?
The challenges faced while working on Vue.js projects are highly dependent on one's specific work experience and the technology involved. You should explain any relevant challenges you encountered related to Vue.js during your previous projects.
3. What was your role in the last Project related to Vue.js?
This question is commonly asked in interviews to understand your specific responsibilities and the functionalities you implemented using Vue.js in your previous projects. Your answer should highlight your role, the tasks you were assigned, and the Vue.js features or techniques you utilized to accomplish those tasks.
4. How much experience do you have in Vue.js?
Here you can tell about your overall work experience on Vue.js.
5. Have you done any Vue.js Certification or Training?
Whether a candidate has completed any Vue.js certification or training is optional. While certifications and training are not essential requirements, they can be advantageous to have.
We have covered some frequently asked Vue.js Interview Questions and Answers to help you for your Interview. All these Essential Vue.js Interview Questions are targeted for mid level of experienced Professionals and freshers.
While attending any Vue.js Interview if you face any difficulty to answer any question please write to us at info@qfles.com. Our IT Expert team will find the best answer and will update on the portal. In case we find any new Vue.js questions, we will update the same here.