How to Build Web Projects Directly Within the Web Browser

A comprehensive guide to building, compiling, and running web applications entirely within your browser using WebAssembly technology.

Written by Chris 6/10/2025

Web Project Preview Directly in the Browser

As part of our development of CodeVideo Studio, we have created a way to preview directly in the browser the project content of any CodeVideo lesson itself, allowing educators to show a preview of what their building, quite literally as they are building it. We'd like to share out findings and techniques with the community, so you can also take advantage of this technology.

Building web applications traditionally requires installing Node.js, setting up build tools, and managing dependencies. This guide shows you how to build, compile, and run web projects entirely within your browser using CodeVideo WebAssembly* technology.

From your side? You only need to declare a external-web-preview action step, and your web project will be compiled and previewed in real-time, right in the browser, or in other words, directly in your CodeVideo video lessons.

_{*Specifically, the esbuild-wasm package.}

What is Browser-Based Web Development?

Browser-based web development means writing, compiling, and running web applications entirely within the web browser itself - no local development environment needed. This is made possible through WebAssembly (WASM), which allows compilation processes to run at near-native speed directly in the browser.

Core Components

In-browser code editors with syntax highlighting
WebAssembly-powered compilers (TypeScript, JSX, etc.)
Virtual file systems in browser memory
Live preview showing real-time results

Why Build Web Projects in the Browser?

Zero Setup Time

Start coding immediately without installing anything. Useful for:

Quick prototypes
Learning web development
Teaching workshops
Collaborative coding

Universal Access

Works on any device with a modern browser:

Chromebooks
iPads
Corporate machines with installation restrictions

Consistent Environment

Everyone gets the same development environment. No "works on my machine" problems.

Key Technologies

WebAssembly (WASM)

The foundation that makes browser-based compilation possible:

Near-native performance
Secure sandboxed execution
Support for multiple languages

esbuild-wasm

Fast JavaScript/TypeScript bundler compiled to WebAssembly:

Supports JSX/TSX transformation
Tree shaking and minification
Used in CodeVideo's WebPreview

Step-by-Step Implementation

Method 1: Using CodeVideo Studio

Navigate to https://studio.codevideo.io
Create any series of web files (HTML, JS, CSS)
- Example: index.html, app.js, styles.css
- Use the built-in editor with syntax highlighting
Preview the web project with the external-web-preview action name. You'll see the live preview of your web application diretly in CodeVideo Studio

Method 2: Building Your Own Browser IDE

Here's a minimal implementation:

1. Set Up Virtual File System

const files = new Map([
  ['/index.html', '<!DOCTYPE html><html>...</html>'],
  ['/app.js', 'console.log("Hello")'],
  ['/styles.css', 'body { margin: 0; }']
]);

2. Initialize esbuild-wasm

import * as esbuild from 'esbuild-wasm';

await esbuild.initialize({
  wasmURL: 'https://unpkg.com/esbuild-wasm@0.25.5/esbuild.wasm',
  worker: false
});

3. Create Virtual File System Plugin

const virtualPlugin = {
  name: 'virtual-fs',
  setup(build) {
    build.onResolve({ filter: /.*/ }, args => {
      if (files.has(args.path)) {
        return { path: args.path, namespace: 'vfs' };
      }
    });
    
    build.onLoad({ filter: /.*/, namespace: 'vfs' }, args => {
      return { contents: files.get(args.path), loader: 'jsx' };
    });
  }
};

4. Bundle and Display

const result = await esbuild.build({
  entryPoints: ['/app.js'],
  bundle: true,
  plugins: [virtualPlugin],
  write: false
});

iframe.srcdoc = `
  <html>
    <body>
      <script>${result.outputFiles[0].text}</script>
    </body>
  </html>
`;

Method 3: Existing Platforms

Several other platforms also offer browser-based development:

CodeSandbox - Full IDE with npm support
StackBlitz - Runs Node.js in browser
CodePen - Quick experiments
Repl.it - Multi-language support

Multi-Language Support

Beyond JavaScript, you can compile other languages:

Python: Pyodide (10MB, includes scientific stack)
Go: Hackpad or native WASM support
Rust: wasm-pack for Rust to WASM
Java: CheerpJ (100MB for JVM)
C/C++: Emscripten or clang-in-wasm

CodeVideo Studio currently only supports JavaScript, TypeScript, and JSX/TSX, with plans to expand to more languages.

Common Issues and Solutions

Q: How fast is browser compilation?

WebAssembly tools like esbuild-wasm are typically 50-80% as fast as native. For most web projects, this is more than adequate.

Q: What about Node.js APIs?

Browser environments can't access Node.js APIs. Use browser-compatible alternatives or polyfills.

Q: Memory limitations?

Browsers typically limit tabs to 2-4GB of memory. For larger projects, implement memory monitoring.

Practical Example: React App

Here's a complete example of compiling a React app in the browser:

// File system
const files = new Map([
  ['/App.jsx', `
    import React from 'react';
    export default function App() {
      return <h1>Hello from browser!</h1>;
    }
  `],
  ['/index.jsx', `
    import React from 'react';
    import ReactDOM from 'react-dom';
    import App from './App';
    
    ReactDOM.render(<App />, document.getElementById('root'));
  `],
  ['/index.html', `
    <!DOCTYPE html>
    <html>
      <head><title>React App</title></head>
      <body><div id="root"></div></body>
    </html>
  `]
]);

// Compile and run
const result = await esbuild.build({
  entryPoints: ['/index.jsx'],
  bundle: true,
  format: 'iife',
  plugins: [virtualPlugin],
  external: ['react', 'react-dom']
});

Conclusion

Building web projects within the browser is practical today. Whether for education, prototyping, or development, browser-based coding environments offer real advantages. The technology continues to improve, with better performance and broader language support coming regularly.

Start building your web projects directly in the browser - no downloads, no setup, just code.

Visit CodeVideo Studio to try browser-based development today.

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