Building a Custom JavaScript Framework from Scratch

This guide provides a step-by-step approach to building your own JavaScript framework, a valuable exercise for deepening your understanding of popular libraries like React, Vue, and Angular.

Core Framework Components:

Most frameworks manage: DOM manipulation, state management, component-based architecture, and event handling. Building a basic framework offers practical experience with these core concepts.

Project Setup:

Begin by structuring your project:

<code>my-js-framework/
│── index.html
│── framework.js
│── app.js</code>

• index.html: The main HTML file.
• framework.js: Your custom framework code.
• app.js: A test file to validate framework functionality.

Implementing Reactivity:

A crucial aspect of modern frameworks is reactivity. Let's create a simple state management system:

<code class="language-javascript">class Reactive {
  constructor(value) {
    this._value = value;
    this.subscribers = new Set();
  }

  get value() {
    return this._value;
  }

  set value(newValue) {
    this._value = newValue;
    this.subscribers.forEach(fn => fn());
  }

  subscribe(fn) {
    this.subscribers.add(fn);
  }
}</code>

This enables components to update automatically when the state changes.

Virtual DOM and Rendering:

Instead of direct DOM manipulation, we'll implement a basic virtual DOM:

<code class="language-javascript">function createElement(tag, props, ...children) {
  return { tag, props, children };
}

function renderElement(node) {
  if (typeof node === "string") return document.createTextNode(node);

  const el = document.createElement(node.tag);
  if (node.props) {
    Object.entries(node.props).forEach(([key, value]) => el.setAttribute(key, value));
  }

  node.children.map(renderElement).forEach(child => el.appendChild(child));
  return el;
}

function mount(vnode, container) {
  container.appendChild(renderElement(vnode));
}</code>

This allows rendering like this:

<code class="language-javascript">const app = createElement("h1", {}, "Hello, World!");
mount(app, document.getElementById("root"));</code>

This will render <h1>Hello, World!</h1> to the page.

Component System:

For modularity, let's add basic component support:

<code class="language-javascript">class Component {
  constructor(props) {
    this.props = props;
  }

  render() {
    return createElement("div", {}, "Default Component");
  }
}</code>

This Component class can be extended to build custom components.

Performance Enhancements:

For efficiency, frameworks utilize diffing algorithms to update only modified DOM parts. While a complete diffing system is complex, you can start by comparing old and new virtual DOM trees and selectively updating changed elements.

Framework Application in PDF Tools:

Integrating a JavaScript framework into web-based PDF tools streamlines UI updates and improves performance. For instance, in a PDF editor, reusable components can be created for file uploads, text annotations, and dynamic PDF rendering.

Conclusion:

You've now created a foundational JavaScript framework with reactive state, a virtual DOM, and component support. While simplified, this provides valuable insight into how modern frameworks function. Further enhancements could include routing, lifecycle hooks, and more sophisticated DOM diffing.

The above is the detailed content of Building a Custom JavaScript Framework from Scratch. For more information, please follow other related articles on the PHP Chinese website!