JavaScript frameworks and libraries are invaluable for building modern web applications. They provide structure, efficient rendering, state management, routing, and other functionality out of the box so you can focus on your app logic and UI. In this comprehensive guide, we will compare popular JavaScript frameworks like React, Vue, Angular, Svelte, Ember, and Meteor.

React

React was created by Facebook and has gained massive popularity due to its performance and flexibility.

Key Features

• Uses virtual DOM for optimized rendering.

• Declarative component architecture to build UI.

• Unidirectional data flow between components.

• Hooks for state and lifecycle methods without classes.

Let's look at a simple React component:

// App.js
import React from 'react';

function App() {
  return (
    <div>
      <h1>Hello World</h1>
    </div>
  );
}

export default App;

We write components using JSX which combines HTML and JavaScript. React has a steep learning curve but allows building complex UIs by composing reusable components.

When to Use React?

React is a good choice when you need:

• A web app with dynamic, interactive UI.

• Excellent performance through virtual DOM.

• Flexible component architecture.

• Abstraction from DOM manipulation.

• Capabilities of JavaScript instead of templating.

Tips for Learning React

• Get comfortable with JSX syntax and component structure.

• Understand unidirectional data flow.

• Master hooks for stateful components.

• Look into React Router for navigation.

• Use React DevTools browser extension.

Vue

Vue was created by Evan You and has rapidly grown to become a popular framework due to its simplicity and approachability.

Key Features

• Uses virtual DOM for high performance.

• Reactive data binding with plain JavaScript.

• Template-based syntax for declarative rendering.

• CSS scoped styles for component modularity.

• Lightweight yet fully capable.

Here's a simple Vue component:

<!-- App.vue -->
<template>
  <h1>{{ message }}</h1>  
</template>

<script>
export default {
  data() {
    return {
      message: 'Hello World'
    }
  }
}
</script>

<style scoped>
h1 {
  color: green; 
}
</style>

Vue combines HTML, JavaScript and CSS in single .vue files. It has a gentle learning curve but can also build complex applications.

When to Use Vue?

Vue is a good choice when you need:

• An approachable framework that is beginner-friendly.

• Template-based structure for defining UI.

• Two-way declarative data binding.

• Ability to progressively add complexity.

• Good documentation and ecosystem.

Tips for Learning Vue

• Understand components, data, methods structure.

• Use v-bind, v-model directives for data binding.

• Learn single file components (.vue) structure.

• Check out Vue Router for SPA navigation.

• Use Vue DevTools browser extension.

Angular

Angular is a TypeScript-based framework built by Google. It follows the model–view–controller (MVC) architecture.

Key Features:

• Two-way declarative data binding.

• Powerful CLI for project generation.

• Excellent tools for routing, forms, HTTP.

• Extensive documentation and community.

• Steeper learning curve.

Here is a simple Angular component:

// app.component.ts

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

@Component({
  selector: 'app-root',
  template: `
    <h1>{{title}}</h1>
  `
})
export class AppComponent {
  title = 'Hello World';
}

Components are classes decorated with @Component metadata. The CLI handles project scaffolding. Angular has excellent tooling but more ceremony compared to Vue and React.

When to Use Angular?

Angular is a good choice when you need:

• Strong foundations with TypeScript static typing.

• Component-based architecture.

• Two-way declarative data binding.

• Excellent tools for animation, forms, routing etc.

• Framework best practices built-in.

Tips for Learning Angular

• Get comfortable with TypeScript.

• Understand dependency injection system.

• Use Angular CLI for project generation.

• Learn directives like ngIf, ngFor for templating.

• Understand services for sharing data.

Svelte

Svelte is a new framework that compiles components into highly optimized vanilla JavaScript.

Key Features:

• Compiles UI components to minimal code.

• Reactive declarative data bindings.

• No virtual DOM due to minimal runtime.

• Small bundle sizes resulting in fast performance.

A Svelte component:

<!-- App.svelte -->

<h1>Hello {name}!</h1>

<script>
let name = 'John'; 
</script>

Write minimal component markup and let Svelte handle compilation. Great performance with a smaller learning curve.

When to Use Svelte?

Svelte is a good choice when you need:

• Blazing fast performance.

• No virtual DOM overhead.

• Small bundle size.

• Reactive data bindings.

• Simple template syntax.

Tips for Learning Svelte

• Understand reactive data bindings.

• Use directives like bind: this and on:event.

• Learn transitions for animation.

• Explore component slots for content projection.

Ember

Ember is a full-featured opinionated framework that follows the model-view-controller pattern.

Key Features:

• Two-way data bindings between models and views.

• Router service for building single page applications.

• Templating language called Handlebars.

• Large ecosystem of addons and libraries.

A simple Ember component:

<!-- app/components/my-component.hbs -->

<h1>{{title}}</h1>

// app/components/my-component.js
export default Component.extend({
  title: 'Hello World' 
});

Ember has batteries-included architecture but a steep learning curve. It enforces conventions so apps are structured similarly.

When to Use Ember?

Ember is a good choice when you need:

• An opinionated framework with conventions.

• Two-way declarative data binding.

• Built-in architectural patterns.

• Large ecosystem of addons.

• Highly structured applications.

Tips for Learning Ember

• Understand Ember's MVC patterns.

• Use Ember CLI tooling.

• Learn Ember data for predictable data management.

• Understand computed properties, helpers.

• Build addons to extend Ember.

Meteor

Meteor is a full-stack JavaScript framework for building reactive real-time web and mobile apps.

Key Features:

• Reactive data bindings to build interactive UIs.

• Full stack - everything from database to UI layers.

• Live page updates using DDP protocol over WebSockets.

• Integrated build system and package manager.

A simple Meteor application:

// app.js
import { Meteor } from 'meteor/meteor';

Meteor.startup(() => {
  // code runs on server at startup  
});

// index.html
<head>
  <title>My App</title>
</head>

<body>
  <h1>Welcome to Meteor!</h1> 
</body>

Meteor handles everything from database to live subscriptions to optimize real-time apps.

When to Use Meteor?

Meteor is great for:

• Real-time collaborative apps with live sync.

• Prototyping and rapid application development.

• Full stack JavaScript projects.

• Eliminating boilerplate code.

Tips for Learning Meteor

• Follow the official tutorial to build an app.

• Understand Publications and Subscriptions.

• Use Meteor CLI for project scaffolding.

• Integrate React components.

• Deploy easily using Galaxy hosting.

So in summary, consider your app requirements and team skills when choosing a JavaScript framework. Each framework has strengths for building web applications. The key is to pick one and dive in to start learning and prototyping your application!