Vue.js Interview Questions and Answers

This section covers frequently asked Vue.js interview questions.

1. What is Vue.js?

Vue.js is a progressive JavaScript framework for building user interfaces and single-page applications. It's known for its ease of use, flexibility, and performance.

2. Why is Vue.js Called a Progressive Framework?

Vue.js is called progressive because it can be adopted incrementally; you can start with a small core and gradually add more features as needed. It's also continuously evolving.

3. Vue.js as a Competitor to Angular.

Vue.js and Angular are both JavaScript frameworks for building user interfaces. Vue.js is rapidly gaining popularity due to its ease of use, flexibility, and performance, making it a strong competitor to Angular.

4. Founder of Vue.js.

Evan You.

5. Vue-Resource Plugin.

Vue-resource is a plugin simplifying HTTP requests. Install it using:

npm install vue-resource --save

yarn add vue-resource

6. Installing Vue.js.

(This section would detail methods for installing Vue.js, including CDN inclusion and using package managers like npm or yarn.)

7. The Next Difference Between Promises and Observables.

Promises are always asynchronous, even if they resolve immediately. Observables can be synchronous or asynchronous.

8. What are Mixins in Vue.js?

Mixins provide a way to reuse code across components. They're particularly useful for sharing functionality or styles.

9. Vuex.

Vuex is a state management library for Vue.js, providing a centralized store for application data and making state changes more predictable.

10. Filters in Vue.js.

Filters format or transform data displayed in templates (mustache interpolations and v-bind expressions). They don't modify the underlying data.

11. Usages of Filters.

• Data formatting for display.
• Improved presentation.
• Code reusability.

12. Components Props.

Props pass data from a parent component to a child component. They're read-only within the child component.

<template>
  
</template>

<script>
export default {
  props: ['postTitle']
}
</script>

13. Calling REST APIs from Vue.js.

Use libraries like Axios to make HTTP requests to REST APIs.

axios.get('/api/users')
  .then(response => {
    this.users = response.data;
  });

14. Deploying Vue.js Applications.

(This section would cover the build process and deployment of a Vue.js application, likely using a bundler like webpack.)

15. Vue-Loader.

Vue-loader is a Webpack loader processing .vue single-file components (containing template, script, and style sections).

16. Handling Events in Vue.js.

(This section would provide code examples showing event handling in Vue.js, typically using the `v-on` directive.)

17. Conditional Directives in Vue.js.

• v-if: Conditionally renders an element.
• v-else: Used with v-if.
• v-else-if: Used with v-if for multiple conditions.
• v-show: Shows or hides an element based on a condition (using CSS display property).
• v-model: Two-way data binding
• v-on: Event handling

18. v-show vs. v-if.

19. Keys in Vue.js.

Keys are used by Vue to track components across updates, improving performance and ensuring that changes are applied correctly.

20. v-if and v-for Together.

Avoid using v-if and v-for on the same element. Refactor to improve performance and clarity.

21. Types of Vue.js Directives.

• General directives
• Literal directives
• Empty directives
• Custom directives

22. Array Mutation Methods

This section would list array methods that trigger Vue's reactivity system. These methods are designed to modify the array and automatically notify the system of changes. Some common array mutation methods include:

• push(): Adds one or more elements to the end of an array.
• pop(): Removes the last element from the array.
• shift(): Removes the first element from the array.
• unshift(): Adds one or more elements to the beginning of the array.
• splice(): Adds or removes elements at a specific index.
• sort(): Sorts the array elements in place.
• reverse(): Reverses the order of the array elements.

Using these methods ensures that any changes to the array are reflected in the Vue.js UI as part of its reactivity system.

27. Array Detection Non-mutation Methods.

These methods don't change the original array but return a new array:

• filter()
• concat()
• slice()

28. Event Modifiers in Vue.js.

Event modifiers in Vue.js modify event handling behavior. They're added as suffixes to the v-on directive:

• .stop: Prevents event propagation.
• .prevent: Prevents default behavior.
• .capture: Handles events during the capture phase.
• .self: Handles events only if triggered on the element itself.
• .once: Handles the event only once.
• .passive: Improves scrolling performance.

29. Event Handlers.

<button v-on:click="handleClick">Click Me</button>

<script>
export default {
  methods: {
    handleClick(event) {
      console.log('Button clicked!', event);
    }
  }
};
</script>

30. Custom Key Modifier Aliases.

Define custom key codes using Vue.config.keyCodes.

Vue.config.keyCodes.myCustomKey = 123;

31. System Modifier Keys.

• .ctrl
• .alt
• .shift
• .meta

32. Local Component Registration.

Register components locally within a component's components option to avoid unnecessary code in the final build.

33. Mouse Button Modifiers.

• .left
• .right
• .middle

34. v-model Modifiers.

• lazy: Syncs input with data on change events instead of input events.
• number: Type-casts input to a number.
• trim: Removes whitespace from input.

35. Single Root Element Requirement.

In Vue 2.x, templates must have a single root element. Vue 3.x supports multiple root elements using fragments (<template>).

36. Global Component Registration.

Register components globally using Vue.component() to make them available in any component within your application.

37. The v-for Directive.

v-for iterates over arrays or objects to render lists of elements.

38. Reusing Elements with the key Attribute.

The key attribute helps Vue.js efficiently update lists by identifying each item uniquely. This is especially important when items are reordered or their position in the array changes. Without keys, Vue.js might not update elements correctly.

39. Importance of key Attribute with v-for.

Using keys helps Vue.js efficiently update lists by tracking individual items.

40. Array Detection Non-Mutation Methods (Repeated from earlier).

Methods like `filter()`, `concat()`, and `slice()` return new arrays without modifying the originals.

41. Redirecting to Another Page.

Use the this.$router.push() method (if using Vue Router).

42. Slots in Vue.js.

Slots provide content distribution outlets within components, allowing you to customize a component's content from its parent.

43. Problems Solved by Single File Components.

• Improved component organization.
• Better syntax highlighting for templates.
• Support for CSS within the component file.
• Integration with preprocessors.

44. Defining Filters in Vue.js.

Filters can be defined locally or globally.

45. mapState Helper in Vuex.

The mapState helper simplifies accessing Vuex store state within components. It generates computed properties that automatically reflect changes in the store's state. This eliminates repetitive code and keeps your components cleaner.

import { mapState } from 'vuex';

export default {
  computed: mapState({
    userName: state => state.user.name,
    userAge: 'user.age' //Shorthand
  })
};

46. Prominent Features of Stylelint.

• Many built-in rules for enforcing style guidelines.
• Supports modern CSS syntax.
• Extracts styles from various sources (HTML, markdown, CSS-in-JS).
• Supports various preprocessors (Sass, Less, etc.).
• Extensible via plugins.

47. Single-File Components in Vue.js.

Single-file components (.vue files) combine a component's template, script (JavaScript), and styles into a single file, improving organization and maintainability.