Comparing JavaScript Frameworks: Svelte, Vue, React and Angular

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JavaScript frameworks are libraries that provide structure and organization for frontend code. They handle aspects like rendering UI, reactivity, state management, routing and have pre-built components. Using a framework can significantly speed up development of web apps. This article compares Svelte, Vue, React and Angular on metrics like reactivity, components, learning curve, scalability and popularity.

Reactivity

Reactivity refers to how frameworks update the UI when the state changes. Most frameworks use a Virtual DOM, a JavaScript representation of the real DOM. When state changes, the Virtual DOM re-renders and calculates the minimal DOM manipulations required to update the UI. This makes reactivity efficient.

Svelte has reactivity built-in and does not use a Virtual DOM. State changes directly update the DOM. This makes reactivity very fast but cannot do optimisations that a Virtual DOM provides.

<script>
  let count = 0;
</script>

<h1>The count is {count}</h1>

<button on:click={() => count++}>Increment</button>

Vue has a Virtual DOM and detects state changes using Proxy-based observation. When state mutates, the Virtual DOM re-renders and Vue updates the real DOM.

data: {
  count: 0
}

template: <h1>{{ count }}</h1> 

methods: {
  increment() {
    this.count++;
  }
}

React has a Virtual DOM and state changes trigger re-renders using setState().Only elements whose state has changed are updated in the real DOM.

class Counter extends React.Component {
  state = { count: 0 };

  increment = () => {
    this.setState({ count: this.state.count + 1 });
  };

  render() { 
    return <h1>{this.state.count}</h1>;
  } 
}

Angular uses a hierarchical change detection system. When state changes, Angular triggers change detection in that subtree and re-renders elements as needed. This is efficient but complex to understand.

@Component({
  selector: 'counter',
  template: '<h1>{{count}}</h1>' 
})
export class Counter {
  count = 0; 

  increment() {
    this.count++;
  } 
}

Components

Components are independent, reusable UI elements that when combined form complex UIs. They have their own state, UI and logic.

Svelte has native support for components with props, scoped styles and lifecycle events. Nested components inherit scope from parents.

<script>
  export let name;

  const handleClick = () => {
    alert(`Hello ${name}!`);
  }
</script>

<button on:click={handleClick}>
  Hello {name}
</button>

<style>
  button {
    color: blue;
  }
</style>

Vue has a robust component system with props, slots, events, lifecycle hooks and scoped styles. Parent and child components communicate via props.

<template>
  <button @click="handleClick">
    <slot></slot>
  </button>
</template>

<script>
export default {
  name: 'HelloButton',
  props: ['name'],
  methods: {
    handleClick() {
      alert(`Hello ${this.name}!`);
    }
  }
}
</script>

<style scoped>
button {
  color: blue; 
}
</style>

React uses components, props and state to build encapsulated, reusable UI elements. Class components have lifecycle methods for updating. Function components are simpler.

class HelloButton extends React.Component {
  handleClick = () => {
    alert(`Hello ${this.props.name}!`);
  }

  render() { 
    return <button onClick={this.handleClick}>{this.props.children}</button> 
  }
}

function HelloButton(props) {
  const handleClick = () => alert(`Hello ${props.name}!`);

  return <button onClick={handleClick}>{props.children}</button> 
}

Angular has components, inputs, outputs, views, templates and services. Components communicate via a hierarchical injection system. The component tree defines scope inheritance.

@Component({
  selector: 'hello-button',
  template: '<button (click)="handleClick()"><ng-content></ng-content></button>'
})
export class HelloButton {
  @Input() name: string;

  handleClick() {
    alert(`Hello ${this.name}!`);
  } 
}

Learning Curve and Scaling

Svelte has a gentle learning curve due to its simplicity but limited scaling options. It suits small apps and prototypes.

Vue is easy to pick up and also scales well to large apps with its robust ecosystem (Vuex, Vue Router). The documentation is very detailed. There is a large talent pool and many job opportunities.

React has a medium learning curve and a huge ecosystem to build large apps (Redux, React Router). Facebook’s backing inspires confidence and there are many resources and jobs.

Angular has a steep learning curve due to its complexity but scales very well for enterprise usage. The documentation is comprehensive but the API is vast. Talent can be harder to find but pays well.

Popularity and Use Cases

Svelte is new and gaining popularity, best for small projects. Vue and React dominate for most use cases. Angular is popular for enterprise applications.

Overall, I would recommend:

• Svelte for prototypes or small apps. Very fast development but limited scaling.
• Vue as an easy to learn yet scalable framework for most projects.
• React for very large apps, especially where performance is a concern. Steep learning curve but powerful.
• Angular for highly complex enterprise systems where longer development time is acceptable. Hard to master but robust.

In summary, the choice of framework depends on priorities like ease of use, performance, scalability and use case. There are great options for projects of all sizes so you can pick a framework suited to your needs.