Vue.js is a progressive JavaScript framework used for building user interfaces and single-page applications. It is designed to be incrementally adoptable, meaning that it can be used for simple projects or scaled up to manage complex applications.

Vue.js is lightweight and provides a simpler API compared to Angular. Unlike React, Vue.js offers a more opinionated structure with a built-in reactivity system, while React relies on an external state management solution like Redux.

The Vue instance is the core of any Vue application. It is an object created using the new Vue() constructor that serves as the root of a Vue app, managing data, methods, and the DOM.

JavaScript:

var vm = new Vue({

  el: '#app',

  data: {

    message: 'Hello Vue!'

  }

});

The el option in a Vue instance binds the instance to a DOM element, enabling Vue to control that part of the DOM. This is where Vue’s reactivity system becomes active.

Vue.js uses an HTML-based template syntax that allows developers to declaratively bind the rendered DOM to the underlying Vue instance’s data. Templates are compiled into render functions that react to changes in data.

HTML:

<div id="app">

  {{ message }}

</div>

A Vue component is a reusable Vue instance with a name. Components are the building blocks of a Vue.js application and allow you to encapsulate HTML, CSS, and JavaScript code.

JavaScript:

Vue.component('my-component', {

  template: '<div>A custom component!</div>'

});

You pass data to a child component using props. Props are custom attributes registered on the child component.

JavaScript:

Vue.component('child-component', {

  props: ['title'],

  template: '<h1>{{ title }}</h1>'

});

Vue directives are special tokens in the markup that tell the library to do something to a DOM element. They are prefixed with v-, such as v-bind, v-if, v-for, etc.

HTML:

<p v-if="seen">Now you see me</p>

The v-bind directive dynamically binds one or more attributes or a component prop to an expression. It is often used to bind HTML attributes like src, href, or class names.

HTML:

<img v-bind:src="imageSrc">

The v-model directive creates a two-way data binding on form elements like <input>, <textarea>, and <select> in Vue.js. It automatically updates the data when the user interacts with the form.

HTML:

<input v-model="message">

Vue.js handles events using the v-on directive, which listens to DOM events and executes methods when triggered.

HTML:

<button v-on:click="doSomething">Click me</button>

Example:

TypeScript:

import { Component, ChangeDetectionStrategy } from '@angular/core';

@Component({

  selector: 'app-onpush',

  template: '<p>{{ data }}</p>',

  changeDetection: ChangeDetectionStrategy.OnPush

})

export class OnPushComponent {

  data: string = 'Initial Data';

}

Vue Router is the official routing library for Vue.js, enabling the creation of single-page applications with multiple views. It maps components to routes, allowing for navigation between them.

JavaScript:

const routes = [

  { path: '/home', component: Home },

  { path: '/about', component: About }

];

const router = new VueRouter({

  routes

});

Vuex is a state management pattern and library for Vue.js applications. It enables centralized management of application state, allowing for a consistent data flow across components.

JavaScript:

const store = new Vuex.Store({

  state: {

    count: 0

  },

  mutations: {

    increment (state) {

      state.count++

    }

  }

});

Conditional rendering in Vue.js is achieved using directives like v-if, v-else, and v-else-if.

HTML:

<p v-if="seen">Now you see me</p>

<p v-else>Now you don't</p>

Example:

TypeScript:

import { HttpClient } from '@angular/common/http';

import { Injectable } from '@angular/core';

@Injectable({

  providedIn: 'root',

})

export class DataService {

  constructor(private http: HttpClient) {}

  fetchData() {

    return this.http.get('https://api.example.com/data');

  }

}

Slots in Vue.js allow you to compose components by passing content from a parent component to a child component. There are default slots, named slots, and scoped slots.

HTML:

<child-component>

  <template v-slot:default>

    <p>This is passed to the child component.</p>

  </template>

</child-component>

The v-for directive is used to render a list of items by iterating over an array or object. Each iteration can also provide an index.

HTML:

<ul>

  <li v-for="(item, index) in items" :key="index">{{ item }}</li>

</ul>

Vue.js achieves reactivity through a reactive system that tracks changes in data properties using getters and setters. When a property changes, Vue re-renders the component with the updated data.

v-show toggles the visibility of an element by changing its display CSS property, while v-if conditionally renders the element in the DOM. v-show is better for frequent toggles, while v-if is more efficient for elements that don't change often.

Custom directives in Vue.js can be created using the Vue.directive method. They allow you to define custom behavior for a DOM element.

JavaScript:

Vue.directive('focus', {

  inserted: function (el) {

    el.focus();

  }

});

Vue.js lifecycle hooks are methods that allow you to perform actions at specific stages of a component’s lifecycle, such as creation (created), mounting (mounted), updating (updated), and destruction (destroyed).

Form validation in Vue.js can be handled using computed properties or third-party libraries like Vuelidate or VeeValidate. Computed properties can return validation states based on form input.

JavaScript:

computed: {

  isFormValid() {

    return this.name !== '' && this.email !== '';

  }

}

An event bus in Vue.js is an instance of Vue that is used to facilitate communication between sibling components by emitting and listening to events.

JavaScript:

var bus = new Vue();

bus.$emit('my-event', data);

bus.$on('my-event', function (data) {

  // handle the event

});

The key attribute in v-for ensures that Vue correctly identifies each item in a list by providing a unique identifier. This helps Vue optimize the re-rendering of the list.

HTML:

<li v-for="item in items" :key="item.id">{{ item.name }}</li>

Lazy loading routes in Vue.js can be done using dynamic imports with Vue Router, which splits the application into smaller chunks that are loaded on demand.

JavaScript:

const Foo = () => import('./Foo.vue');

const router = new VueRouter({

  routes: [

    { path: '/foo', component: Foo }

  ]

});

Vue CLI is a command-line interface tool for Vue.js that provides a rapid way to scaffold, develop, and manage Vue.js applications. It includes features like a plugin system, a dev server, and build tools.

Filters in Vue.js are used to apply common text formatting within mustache interpolations or v-bind expressions. Filters are usually applied in a Vue template and can be chained.

JavaScript:

Vue.filter('capitalize', function (value) {

  if (!value) return '';

  value = value.toString();

  return value.charAt(0).toUpperCase() + value.slice(1);

});

html

Copy code

<p>{{ message | capitalize }}</p>

A mixin is a reusable block of code that contains component options like data, methods, or hooks, which can be shared across multiple components. When a component uses a mixin, the mixin’s data and methods are merged with the component’s own.

JavaScript:

const myMixin = {

  data() {

    return {

      message: 'Hello from mixin!'

    };

  },

  created() {

    console.log('Mixin hook called');

  }

};

new Vue({

  mixins: [myMixin],

  created() {

    console.log('Component hook called');

  }

});

Computed properties in Vue.js are used to define reactive values that depend on other data properties. They are cached based on their dependencies, and they only re-evaluate when one of the dependencies changes.

JavaScript:

computed: {

  reversedMessage() {

    return this.message.split('').reverse().join('');

  }

}

Vue.js provides an easy way to apply animations when elements enter or leave the DOM. This is done using the transition component and CSS classes like v-enter, v-leave, and others for various stages of the animation.

HTML:

<transition name="fade">

  <p v-if="show">Hello Vue!</p>

</transition>

CSS:

.fade-enter-active, .fade-leave-active {

  transition: opacity 1s;

}

.fade-enter, .fade-leave-to /* .fade-leave-active in <2.1.8 */ {

  opacity: 0;

}

Methods and Computed properties both provide functionality to work with data, but they are used differently:

• Methods: Re-execute every time they are called, regardless of whether their dependencies have changed. Ideal for actions triggered by user events.
• Computed Properties: Cache their results and only re-compute when their dependencies change. Ideal for values that are derived from reactive data.

JavaScript:

computed: {

  fullName() {

    return `${this.firstName} ${this.lastName}`;

  }

},

methods: {

  greet() {

    return `Hello, ${this.fullName}!`;

  }

}