Vue.js interview questions and answers in 2023

This is an important Vue.js interview question. The directive is a piece of markup that tells the library what to do with a certain DOM element. Vue.js comes with a number of built-in directives, such as v-bind and v-model. You can also make your own directions.

Data flow is important for transferring information between components.

Parent Component to Child - 'Props' is used to send data from a parent component to a child component. Props are custom attributes that you may register on a component, and when a value is supplied to those props attributes, that component instance becomes a property. As a result, all modifications made by the parent component are reflected in the prop attribute of the child component.

To handle this problem, Vue instances provide the notion of events. Child Component to Parent - Some scenarios may necessitate communication back to the parent component, hence Vue instances provide the concept of events to solve this case.

The parent component can use 'v-on' to listen to any event on the child component, and the child component can use the $emit method to emit any event.

Data Sharing Across Components - In some cases, data sharing across all components may be essential. Vuex overcomes this challenge by establishing a centralized data store that is accessible to all components.

This is a popular Vue.js interview question. All Props work in one direction, which means data flows from parent to kid. When a modification is made to a parent property, the child property is automatically updated, but not the other way around. It prohibits a child from changing the state of the parent property, which can make your application's data flow more difficult to comprehend.

Data is passed from the parent component to the child component using Component Prop. A component can have as many props as it wants. The prop is a custom attribute that becomes a property on the component instance when a value is supplied to it.

From parent to child component, a component Prop forms a one-way down binding. When the parent property changes, it affects the child, but not the other way around. As a result, when the Parent component is modified, all child components are updated as well. As a result, you won't have to worry about mutating the prop in the child component.

You will often come across this Vue.js interview question. Mixins in Vue.js enable a versatile approach to reuse Vue instances and components' functionality or code. Mixins are stored in a separate file and can be reused across several components. When a component uses a Mixin, the Mixin's choices become part of the component's options, thereby merging them with the component's options.

You may also construct Global Mixins but do so with caution because they will affect any subsequent Vue.js instances.

SFCs, or single file components, are similar to other components in that they are self-contained in their own files. The following are some of the benefits of SFCs.

• Global Definitions - This refers to the fact that all SFCs are registered globally and given unique names.
• Strong Templates - Instead of using a single template property like other components, you can easily create template code in SFCs.
• CSS Support – SFCs allow you to apply CSS to the component itself.
• Support for preprocessors – preprocessors like babel, SAAS, and others can be simply used in SFCs.

This is one of the most asked Vue.js interview questions. In Vue, the key attribute is used as a clue for the virtual DOM technique to distinguish VNodes when creating a new node list from an existing one.

If the 'key' attribute is not utilized, Vue utilizes an algorithm that tries to reuse elements of the same type and reduces element movement. The elements with the 'key' property, on the other hand, will be reordered and the elements without it will be eliminated. It's similar to AngularJS's $index. It's most commonly used in conjunction with the 'v-for' directive.

In Vue, the Document Object Model is represented by the Virtual DOM, which is a JavaScript object (DOM). 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 you pick it, Virtual DOM will just keep the data in its current state without re-rendering it. Virtual DOM can also help you improve the performance of your web apps by reducing the number of times the DOM needs to be updated.

In the child component, $parent is used to retrieve the parent component instance. It's more difficult to test and debug the program, and you can't figure out where the mutation comes from. Vue also has a $child function that returns a child component instance, similar to $parent.

This is a rather popular Vue.js interview question. Jest and Mocha are built-in unit testing tools in the Vue CLI. Jest is a Facebook-developed test runner. It provides a unit-testing solution that is battery-powered. To run Jest tests, use the Vue CLI plugin 'cli-plugin-unit-jest'.

Mocha is a JavaScript-based test framework for asynchronous testing that works on Node.js and in browsers. It includes a built-in webpack precompiler.