Vue.js Interview Questions and Answers for 10 years experience

1. What is Vue.js and what are its core principles?

   • Answer: Vue.js is a progressive JavaScript framework for building user interfaces. Its core principles include: incremental adoption (you can integrate it piecemeal into existing projects), reactive data binding (changes in data automatically update the UI, and vice-versa), component-based architecture (building UIs from reusable components), and ease of learning (it's relatively easy to pick up, especially for developers familiar with JavaScript).

2. Explain the difference between `v-if` and `v-show` directives.

   • Answer: `v-if` conditionally renders an element based on a truthy/falsy value. It completely removes and re-adds the element to the DOM. `v-show` simply toggles the CSS `display` property of the element. `v-if` is better for performance when the condition rarely changes, while `v-show` is better for frequently changing conditions.

3. What are computed properties in Vue.js? Give an example.

   • Answer: Computed properties are dependent on other data properties. They are cached, meaning they only re-compute when their dependencies change. This improves performance. Example: If you have `firstName` and `lastName` data properties, a computed property `fullName` could combine them. The `fullName` only updates when `firstName` or `lastName` changes.

4. What are watchers in Vue.js and when would you use them?

   • Answer: Watchers allow you to react to data changes. Unlike computed properties, they don't cache their results. Use watchers when you need to perform an action based on a data change that doesn't directly affect the template, such as making an API call or updating a third-party library.

5. Explain the Vue.js lifecycle hooks. Name at least five and explain their purpose.

   • Answer: Vue.js lifecycle hooks are methods called at specific stages of a component's lifecycle. Five examples are: `beforeCreate`, `created`, `beforeMount`, `mounted`, and `beforeUpdate`. `beforeCreate` runs before the instance is created. `created` runs after the instance is created. `beforeMount` runs before the component is mounted to the DOM. `mounted` runs after the component is mounted. `beforeUpdate` runs before data updates cause a re-render.

6. How do you handle events in Vue.js? Give an example using `v-on`.

   • Answer: Events are handled using the `v-on` directive (or the shorthand `@`). Example: `Click Me`. The `handleClick` method would be defined in the component's methods object.

7. Explain the concept of props in Vue.js. How do you pass data to a child component?

   • Answer: Props are a way to pass data from a parent component to a child component. They are defined in the child component's `props` option and are read-only in the child component. Data is passed by specifying the prop names and values in the parent component's template when the child component is used.

8. What are slots in Vue.js and how are they used?

   • Answer: Slots allow you to inject content into a component from the parent component. This makes components more reusable. They are defined using `` tags within the child component's template.

9. Describe the different ways to define a Vue.js component.

   • Answer: Vue.js components can be defined in several ways: using the `Vue.component()` global method, using an object literal in a `components` object within a component, using functional components, or via a .vue single-file component.

10. Explain the use of `$nextTick` in Vue.js.

    • Answer: `$nextTick` queues a callback function to be executed after the next DOM update cycle. This is useful when you need to access updated DOM elements after a data change.

11. What is the difference between `methods` and `computed` properties?

    • Answer: Methods are functions that can accept arguments and perform actions, while computed properties are cached and reactive, re-calculating only when their dependencies change. Use computed properties for data transformations that depend on other data; use methods for more complex actions.

12. How do you handle asynchronous operations in Vue.js?

    • Answer: Asynchronous operations, like API calls, are typically handled using `async/await` or promises within methods. You might use a loading state indicator during the operation to provide user feedback.

13. Explain the concept of a Vuex store.

    • Answer: Vuex is a state management library for Vue.js. It provides a centralized store for all components in your application, making it easy to manage state and data flow. It uses concepts like state, getters, mutations, and actions.

14. How do you use Vue Router?

    • Answer: Vue Router is used for client-side routing in Vue.js applications. It allows you to navigate between different views or components using URLs. It involves defining routes and components, and then using `` to render the active component.

15. Explain how to implement form validation in Vue.js.

    • Answer: Form validation can be done using built-in HTML5 validation, custom validation logic within methods, or dedicated validation libraries like Vee-Validate. You can provide feedback to the user through error messages displayed next to the form fields.

16. What are Mixins in Vue.js?

    • Answer: Mixins are a flexible way to distribute reusable functionalities across multiple components. They are essentially objects containing methods, computed properties, data, and lifecycle hooks that can be merged into a component.

17. How do you handle error handling in Vue.js applications?

    • Answer: Error handling involves using try-catch blocks within methods, and global error handling with `Vue.config.errorHandler` or by using a dedicated error boundary component.

18. Describe your experience with testing Vue.js components. What testing frameworks have you used?

    • Answer: [This answer will be specific to the interviewee's experience. It should mention frameworks like Jest, Mocha, Cypress, or others and describe the approaches used, like unit testing, integration testing, and end-to-end testing.]

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