15 most asked Vue.js Interview questions

This article will guide you through the 15 most asked Vue.js Interview questions so as to boost your skills and confidence.

An interview is an important stepping stone to new careers. Therefore, when planning to attend a Vue interview then adequate preparation is essential.

That is to say, that the correct answering of the hiring panel question’s will give you an upper hand of winning that job.

1. What is Vue.JS

Vue.Js is a progressive framework that is used in creating dynamic user interfaces. Moreover, Vue.Js is different from other monolithic frameworks since it designed to be highly adaptable. Generally, Vue is simple thus easy to learn. Its main library is focused on view only, consequently making it easy to integrate with other libraries.

2. Why should arrow functions not be used while writing lifecycle hooks in Vue instance?

Arrow functions are not independent, as a result, they cannot define a ‘this’ of their own. But instead, the arrow functions are bound to their parent’s function’s context.

In a situation where the arrow function (=>) is used in the Vue app, the keyword ‘this’ does not bind to the Vue instance and therefore, resulting in errors.

For that reason, it is highly advised to use the standard function declaration instead of the arrow function.

3. Briefly explain the difference between one-way data flow and two-way data binding?

By definition, one-way data flow means that the model is the only source of truth. While two-way data-binding means that UI fields are found to model data. Therefore, in case UI field changes, the model data also changes and vice-versa.

Secondly, one-way data flows are deterministic, in contrast, the two-way binding is associated with several side effects that are difficult to identify and understand.

Additionally, for one-way data flow, the UI aspect of the application can not update automatically. This, in turn, results in a need to customize certain codes to help it update every time there is a change in the data model. Whereas, in data binding, the UI part of the application usually updates automatically when the data model is changed.

4. Explain Vue.js reactivity and common issues when tracking changes?

Generally, this is a very common Vue interview question. Usually, all properties defined in Vue instance are very reactive. This means that in case of any change, the components automatically update and re-render.

Therefore, all these properties are changed to getters and setters in the inItialization stage. Hence, giving Vue the ability to detect when these properties are changed.

Above all, the following setbacks must be considered while designing a Vue app;

• Because of JavaScript limitation, Vue cannot detect the deletion or addition of an object property.
• Additionally, it cannot also detect the modification of array items, hence, the need to use Vue .set.

5. How can two-way data binding be created in Vue J’s?

Vue’s two-way binding system is among the toughest steps of developing a web application, synchronization of user data although the v-model makes it very simple.

The V-model detective performs a regular update of the templates. The updates occur whenever the model changes and also updates the data model in case the template changes.

Two-way binding is a great and powerful feature that when used appropriately, can significantly boost the speed of the development process. Additionally, in two-way data is bounded to the DOM, which is in turn bound back to the model.

Below is an example of the implementation of two-way binding;

<Dev id="app">
   {{Message}}
  <Input v-model="message">
</Dev>
<Script type="text/javascript">
  Var message = 'Vue. J's is rad';
  New Vue ({ el: '#app', data {{message }};;
</Script>

6. What is a Vue plugin?

Vue plugins are simple but powerful tools that enable developers to build and add global level functionality to Vue.

The Vue plugins have a wide range of uses, for example, distributing app-wide components, the addition of extra features, such as routing and immutable data stores for your apps.

Above all, the Vue plugin is very simple to use since all you need is just to install it. One of the commonly used Vue plugins is the VueFire plugin that adds firebase methods and bindings to the whole application.

7. What are the props of the component?

In Vue.js, each component instance has its own unique isolated scope. Therefore, parent data cannot be directly referenced in a child’s component template.

The props can be used to pass down data to child components. Furthermore, props are custom attributes that can easily be registered on a component.

In a situation where a value is transferred to a prop attribute, it becomes a property of that component instance.

Vue.component('blog-post', {
  // camelCase in JavaScript
  props: ['postTitle'],
  template: '<h3>{{ postTitle }}</h3>'
})

8. What are mixins? Then briefly describe their advantages and disadvantages.

Mixins are flexible methods of redistributing reusable features for Vue components. A mixin object can accommodate any component option. When a component uses a mixin, all mixin components are merged with components options.

Advantages of using

• It has several objects for heap allocation.
• It’s run time assembly can prevent the problem of supporting persistence.
• Additionally, the run time assembly can also lead to objects which seem mysterious.

Disadvantages of using mixins

• It increases dependencies.
• Global mixins affect every component, hence this can result in a serious maintenance problem.

9. State some features of Vue.js?

Vue.js have the following features;

• It has a Virtual DOM.
• It has a data-binding feature which helps in manipulating values to HTML attributes.
• Its components help in creating customized components that are in turn used in HTML.
• The capability of providing a transition to HTML elements.
• Vue.js has HTML based templates.
• Built-in directives such as v-show.
• It has watchers which are applied to data that changes.
• Vue. j’s is a lightweight thus better performance.
• Routing feature which makes it possible to navigate between pages.

10. Which lifecycle hook is best for collecting data from API calls?

This mainly depends on its usage and the purpose of the component. Usually, the newly created lifecycle hook is normally the best for placing an API call. This is because, at this stage, the reactivity features and component data are available to operate despite the fact that the components haven’t rendered yet.

11. How can query parameters be fetched in Vue.js?

Normally, according to the docs of route objects, the $route from the components have to be accessed.

That will lead you to what you need, which is;

//from your component
console.log(this.$route.query.test) // outputs 'yay'

12. What is Virtual Dom and what are some of its benefits?

Virtual DOM is a JavaScript object that helps in representing the Document Object Model (DOM).

Currently, many libraries including Vue implement the idea of Virtual DOM.

The main use of Virtual DOM to quickly and efficiently manipulate the DOM. In a situation where there are several nodes in the DOM, the updating process is very expensive due to resources required and processing power.

Using the virtual DOM JavaScript object is preferably faster and very efficient. Lastly, Vue.js automatically organizes DOM updates in batches, therefore, boosting efficiency.

13. Briefly explain the basic logical Vue.js app organization?

Normally,Vue.js application comprises of a root Vue instance generated with a new Vue, which is organized into a tree of nested, reusable components. Below is a good example, of how a todo app’s component tree might look like;

Root Instance
└─ TodoList
   ├─ TodoItem
   │  ├─ DeleteTodoButton
   │  └─ EditTodoButton
   └─ TodoListFooter
      ├─ ClearTodosButton
      └─ TodoListStatistics

14. What do you understand by the term vue-loader?

By definition, Vue-loader is a loader module for a web pack that supports the writing of a single file component using the Vue file format. A single file component file comprises three sections; template, style, and script.

The Vue-loader module supports web packs in processing and extracting each section using different loader modules, for example, SASS or SCSS loaders. The setup, therefore, accommodates the seamless authoring of apps using Vue files.

Additionally, the Vue-loader module also gives room for static assets to be considered as dependencies and enables processing through webpack loaders. Lastly, it also allows for hot reloading during development.

15. What is the difference between slots and scoped slots?

By definition, a slot is a placeholder in a child component that is full of components passed from the parent. The content of the regular slot is included the parent scope and then transferred to the child component.

For that reason, child component properties cannot be used in the slot’s content. Rather, scoped slots give room to pass component data to the parent scope, thus allowing the use of data in the slot content.

Conclusion

It is my hope that these most asked Vue.js Interview questions and answers give a clear clue of what kind of questions you are likely to meet in the interview room.

There are also several other possible questions that might be through to you, therefore adequate preparation before that interview is essential.

All the best in your interview and feel free to like and drop a comment.