Building a Custom JavaScript Framework from Scratch

Creating your own JavaScript framework might sound overwhelming, but it's an excellent way to sharpen your skills and understand the inner workings of libraries like React, Vue, or Angular. In this guide, we'll break it down step by step.

1. Understanding the Core of a JavaScript Framework
Most JavaScript frameworks handle:

• DOM Manipulation
• State Management
• Component-Based Architecture
• Event Handling

By building a simple framework, you'll get hands-on experience with these concepts.

2. Setting Up the Project
To start, create a basic project structure:

my-js-framework/
│── index.html
│── framework.js
│── app.js

index.html – The main HTML file
framework.js – Our custom JavaScript framework
app.js – A test file to check if our framework works

3. Creating a Simple Reactive System
A key feature of frameworks like Vue and React is reactivity. Let’s implement a simple state management system:

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);
  }
}

This allows components to automatically update when the state changes!

4. Virtual DOM and Rendering
Instead of directly manipulating the DOM, let’s create a simple virtual DOM system:

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));
}

This allows us to write:

const app = createElement("h1", {}, "Hello, World!");
mount(app, document.getElementById("root"));
And it will render <h1>Hello, World!</h1> on the page.

5. Adding Component Support
To make our framework more modular, let's add simple component support:

js
Copy
Edit
class Component {
  constructor(props) {
    this.props = props;
  }

  render() {
    return createElement("div", {}, "Default Component");
  }
}

Now, we can extend this class to create custom components.

6. Optimizing Performance
For better efficiency, frameworks use diffing algorithms to update only the changed parts of the DOM. Implementing a full diffing system is complex, but you can start by comparing previous and new virtual DOM trees and updating only modified elements.

7. Why Optimize Your Framework for PDFs?
If you're building a web-based PDF tool, integrating a JavaScript framework can help streamline UI updates and improve performance. For example, if you're working with a free PDF editing tool, you can create reusable components for file uploads, text annotations, and rendering PDFs dynamically.

8. Finally
Congratulations! You’ve built a basic JavaScript framework with reactive state, virtual DOM, and component support. While this is a simplified version, it gives your insight into how modern frameworks work.

Want to take it further? Try adding:
✔️ Routing (like React Router)
✔️ Lifecycle Hooks
✔️ More Efficient DOM Diffing