1. Understanding Vue.js: Core Features and Browser Compatibility

Vue.js is a progressive framework designed for building user interfaces. Its core architecture centers around a reactive data binding system that automatically synchronizes the view with underlying data changes. As an MVVM pattern implementation, Vue handles the synchronization between the Model and View layers through its internal mechanisms.

Key characteristics include minimalism, data-driven updates, component-based architecture, and modular flexibility.

Vue.js relies on ECMAScript 5 features that cannot be polyfilled, which is why IE8 and earlier versions are not supported.

2. Vue's Reactive Data Binding Implementation

Vue implements two-way data binding by leveraging the Object.defineProperty method to intercept data access and modification operations. This technique, known as data劫持 (data hijacking), allows Vue to detect when properties are read or changed.

When a property is accessed or modified, the custom getter and setter functions execute additional logic, enabling automatic view updates whenever the underlying data changes.

3. MVVM Architecture vs MVC Pattern

MVVM stands for Model-View-ViewModel. The Model represents application data, the View handles UI rendering, and the ViewModel serves as an intermediary that connects Model and View through bidirectional data binding.

Unlike MVC where View and Model are directly connected, MVVM uses the ViewModel as a bridge. Changes in Model automatically propagate to View, and user interactions in View can directly affect Model data.

MVC separates Model and View through a Controller, whereas MVVM provides automatic synchronization between View and Model without manual DOM manipulation when data changes.

4. Vue's Core Concepts

The framework is built on two fundamental principles: data-driven reactivity and component-based development.

5. Vue vs Angular: Key Differences

Vue utilizes ES5 getters/setters for its reactivity system, while Angular implements its own template compilation with dirty checking mechanisms. Vue does not require dirty checking since it tracks dependencies automatically.

Vue requires an el option to specify the mounting element, limiting its scope to that element. Angular operates on the entire document.

6. Vue's Internal Working Mechanism

Vue follows an M-V-VM pattern where the ViewModel acts as the binding layer.

The process involves:

1. Creating a virtual DOM tree using document.createDocumentFragment()
2. Intercepting data changes through Object.defineProperty getters/setters
3. Notifying subscribed Watchers via a publish-subscribe pattern when data mutates
4. Updating virtual DOM nodes and subsequently rendering the actual DOM

7. Single Page Application Characteristics

SPAs deliver all content within a single HTML page, with dynamic updates occurring without full page reloads.

Advantages include smooth user experience without page refreshes, efficient resource loading through single bundle downloads, organized code structure using components, and simplified maintenance.

Disadvantages encompass poor SEO performance, lack of browser history support requiring custom implementation, longer initial load times, and inability to use standard browser navigation buttons.

8. React vs Vue: Comprehensive Comparison

Similarities:

• Both support server-side rendering
• Both implement data-driven UI updates
• Both provide state management solutions
• Both utilize virtual DOM concepts
• Both embrace component-based architecture
• Both enable parent-to-child data passing through props

Differences:

Aspect	React	Vue
Pattern	Primarily Controller in MVC	Full MVVM
DOM Updates	Re-renders entire component tree on state change	Tracks dependencies to selectively update
Template	JSX syntax	Single-file components with template sections
Data Flow	Unidirectional	Bidirectional with v-model
State	Immutable, requires setState()	Reactive, directly modifiable

9. Benefits of Component-Based Architecture

• Accelerated development velocity
• Reusability across different project sections
• Simplified team collaboration
• Improved maintainability and scalability

10. Vue Component Lifecycle Hooks

Creation Phase:

• beforeCreate: Instance initialized, data and DOM unavailable
• created: Data observables active, DOM not yet mounted

Mounting Phase:

• beforeMount: Template compiled, real DOM not yet inserted
• mounted: Component successfully rendered to DOM

Update Phase:

• beforeUpdate: Reactive data changed, re-render triggered
• updated: Component re-rendered with updated data

Destruction Phase:

• beforeDestroy: Cleanup operations before removal
• destroyed: Instance fully removed, DOM elements remain

Keep-alive Enhancement: Components wrapped in keep-alive gain two additional hooks:

• activated: Component re-enters view
• deactivated: Component exits view

11. Angular's Change Detection Mechanism

Angular cannot natively determine whether data has mutated. It periodically triggers a full digest cycle that traverses all data bindings to detect changes. This approach is inefficient as it performs unnecessary comparisons across the entire scope.

12. Scoped Component Styles

Adding the scoped attribute to a style block ensures CSS rules apply exclusively to the current component:

<style scoped>
.card { color: #333; }
</style>

13. v-if vs v-show Directives

Both control element visibility but with different mechanisms:

Aspect	v-if	v-show
Implementation	DOM element creation/destruction	CSS display property toggling
Initial Render	Only when condition is true	Always rendered
Toggle Cost	Higher (DOM manipulation)	Lower (style change)
Use Case	Conditions rarely changing	Frequent visibility toggling

14. Vue Event Modifiers

Event Modifiers: .stop, .prevent, .self, .once

Keyboard Modifiers: .enter, .space, .up, .down

Form Modifiers: .number, .trim, .lazy

15. Common Vue Directives

• v-if, v-show, v-for, v-on, v-bind, v-model, v-once

16. Multiple Event Handlers

Vue allows binding multiple handlers to a single event:

<input @keyup.enter="handleSubmit" @focus="handleFocus">

17. $mount vs el Configuration

Both mount Vue instances to DOM elements with identical functionality. The el option automatically triggers mounting during instance creation, while $mount provides manual control for deferred mounting when el is not specified.

18. Event Modifier Usage

<!-- Prevent event propagation -->
<a @click.stop="handleClick"></a>

<!-- Prevent default form submission -->
<form @submit.prevent="submitForm"></form>

<!-- Chain multiple modifiers -->
<a @click.stop.prevent="handleLink"></a>

<!-- Form with prevent only -->
<form @submit.prevent></form>

<!-- Single-fire event -->
<button @click.once="doOnce"></button>

<!-- Self-targeting only -->
<div @click.self="handleOwnClick">...</div>

19. Key and Is Attributes

The key attribute helps Vue track element identity, enabling efficient reordering and removal of elements during updates.

The is attribute enables dynamic component switching and HTML element extension:

<component :is="currentComponent"></component>
<table><tr is="my-row"></tr></table>

20. Data Must Be a Function in Components

Component data must be a function returning a fresh object because components are designed for reuse. Using a plain object would create shared references across instances, causing data contamination between components.

Vue instances use plain objects since they are not intended for reuse, eliminating this concern.

21. Unidirectional Data Flow

Data flows downward from parent to child components. When a child needs to modify parent data, it emits an event to the parent, which then updates its data and passes the new value back down.

22. Computed Properties

Computed properties automatically track reactive dependencies and recalculate when underlying data changes.

Function Syntax:

computed: {
  totalPrice() {
    return this.items.reduce((sum, item) => sum + item.price, 0);
  }
}

Object Syntax with Getter/Setter:

computed: {
  fullName: {
    get() {
      return this.firstName + ' ' + this.lastName;
    },
    set(newValue) {
      const parts = newValue.split(' ');
      this.firstName = parts[0];
      this.lastName = parts[1];
    }
  }
}

23. Component Communication Patterns

Parent to Child:

Parent passes data via custom attributes bound with v-bind, child receives through props:

<!-- Parent Template -->
<child-component :user-data="userInfo"></child-component>

<!-- Child Component -->
<script>
export default {
  props: ['userData']
}
</script>

Child to Parent:

Child emits custom events with payload, parent listens and responds:

<!-- Child -->
<script>
methods: {
  sendUpdate() {
    this.$emit('data-changed', updatedValue);
  }
}
</script>

<!-- Parent Template -->
<child-component @data-changed="handleUpdate"></child-component>

24. Computed vs Watch

Computed Properties:

• Evaluate immediately on component load
• Re-evaluate whenever any dependency changes
• Ideal for deriving values from existing data
• Can use getters and setters

Watch Properties:

• Do not execute on initial load (configurable)
• Trigger only when the watched variable changes
• Support deep watching and immediate execution options
• Suitable for executing side effects based on data changes

25. Vue.nextTick Usage

nextTick ensures access to updated DOM elements after data changes:

created() {
  this.fetchData().then(() => {
    this.$nextTick(() => {
      // Safe to access DOM here
      this.initializePlugin();
    });
  });
}

Essential when performing DOM operations in created() hook since DOM hasn't rendered yet at that stage.

26. Custom Directives

Global Registration:

Vue.directive('focus', {
  bind(el, binding) { /* Initial setup */ },
  inserted(el, binding) { /* DOM insertion */ },
  update(el, binding, oldValue) { /* Component updates */ }
});

Component-local Registration:

directives: {
  check: {
    bind(el, binding) { /* binding.value */ }
  }
}

Hook parameters include el (DOM element) and binding (directive configuration object).

27. Optimizing SPA Initial Load

• Load vendor libraries from CDN for parallel downloading
• Implement lazy loading for routes and components
• Display loading indicators during initial fetch

28. Form Modifier Functions

trim: Strips leading and trailing whitespace from input

number: Casts bound value to numeric type

lazy: Switches synchronization from input events to change events

29. Vue Router Navigation Guards

Global Guards: to, from, next parameters

In-component Guards:

• beforeRouteEnter
• beforeRouteUpdate
• beforeRouteLeave

Per-route Guards: beforeEnter

30. Navigation Methods

Declarative:

<router-link :to="{ name: 'dashboard' }"></router-link>

Programmatic:

this.$router.push({ path: '/dashboard' });

31. Route-based Code Splitting

Webpack's require.ensure enables on-demand loading:

Standard Import:

import UserSettings from './views/Settings.vue';

Lazy Loading:

const Settings = r => require.ensure([], () => r(require('./views/Settings.vue')));

32. $router vs $route

$router: The VueRouter instance, provides navigation methods and instance properties

$route: The current route object containing name, path, params, query, meta, and hash properties

33. vue-loader Functionality

vue-loader transforms .vue single-file components into JavaScript modules. It enables:

• ES6 syntax in script sections
• SCSS/LESS preprocessing in style sections
• Jade/Pug templating in template sections

34. Query Parameters vs Route Params

Aspect	params	query
Definition	Path parameters	URL query string
Syntax	Named routes only	Path-based
Visibility	Hidden in URL	Visible in URL
Behavior	Similar to POST	Similar to GET

35. Dynamic Route Configuration

Define dynamic segments with colon notation:

{ path: '/user/:userId', component: UserProfile }

Access via this.$route.params.userId

36. Nested Route Definitions

The children property enables hierarchical routing:

{
  path: '/dashboard',
  component: Dashboard,
  children: [
    { path: 'statistics', component: Stats },
    { path: 'reports', component: Reports }
  ]
}

37. active-class Implementation

This router-link property applies CSS classes to active navigation links.

38. Route Object Properties

Property	Purpose
$route.name	Current route identifier
$route.path	Current route path
$route.meta	Metadata for route authentication
$route.query	Query string parameters
$route.hash	URL fragment identifier
$route.params	Path parameter values

39. src Directory Structure

• main.js: Application entry point
• App.vue: Root application component
• views/: Page-level components
• components/: Reusable UI components
• router/: Navigation configuration
• assets/: Static resources like images and fonts

40. Component Import Workflow

1. Create component file in components directory
2. Import into the using component
3. Register in the components option
4. Use in template markup

41. Component Lifecycle Purpose

Lifecycle hooks provide execution points throughout the component's existence:

• Instantiation
• Data initialization
• Template compilation
• DOM mounting
• Updates and re-renders
• Cleanup and removal

Initial page load triggers: beforeCreate, created, beforeMount, mounted

42. Lifecycle Hook Selection Guide

• beforeCreate: Initialize loading states
• created: Fetch initial data, complete loading indicators
• mounted: DOM manipulation (prefer nextTick for timing)
• updated: Centralized data processing
• beforeDestroy: Clear intervals, remove event listeners
• destroyed: Complete cleanup operations

43. Slot Content Distribution

Slots provide fallback content placement within components:

<!-- Component Template -->
<div class="container">
  <slot>Default fallback content</slot>
</div>

<!-- Usage -->
<my-component>Custom content</my-component>

Unnamed slots receive default slot content. Named slots handle specific content regions.

44. Computed, Watch, and Methods Comparison

Computed Options: get, set

Watch Options: handler, deep, immediate

Methods vs Computed:

• Methods accept parameters, computed cannot
• Computed results are cached, methods execute on each call
• Computed can depend on other computed properties and component data

45. Render Functions

When template syntax is insufficient, the render function creates VNodes programmatically:

render(createElement) {
  return createElement('div', {
    class: 'wrapper'
  }, [
    createElement('h1', this.title),
    createElement('p', this.content)
  ]);
}

These VNodes form the virtual DOM tree for efficient updates.

46. Vuex State Management

Vuex centralizes application state in a single accessible store:

// store/index.js
import Vue from 'vue';
import Vuex from 'vuex';

Vue.use(Vuex);

export default new Vuex.Store({
  state: { user: null },
  mutations: { setUser(state, payload) { state.user = payload; } },
  actions: { fetchUser({ commit }) { /* API call */ } }
});

Use Cases: User authentication, shopping cart, media playback controls

47. nextTick Requirement in created Hook

The created hook executes before DOM rendering completes, making any DOM manipulation ineffective. Wrap DOM-dependent code in nextTick callbacks to ensure execution after the DOM updates.

48. Vuex Store Properties

The store maintains reactive state. Component computed properties automatically sync with store data. Mutations trigger reactive updates across all dependent components. Helper functions map state and getters to local computed properties.

49. AJAX Request Placement

In Component Methods: When data serves only that component

In Vuex Actions: When data requires sharing across components or needs caching for reuse. Actions return Promises enabling composition.

50. Vuex Data Flow

1. User interaction triggers action via dispatch
2. Action executes logic and commits mutation
3. Mutation synchronously updates state
4. State changes propagate to components
5. Components retrieve updated data and re-render