WebAssembly and JavaScript: A Synergistic Relationship

A common misconception is that WebAssembly (Wasm) aims to replace JavaScript. In reality, Wasm is designed to complement JavaScript, allowing developers to leverage the strengths of both technologies to build more powerful and performant web applications.

Designed to Work Together

The WebAssembly specification includes a JavaScript API that enables:

• Loading Wasm Modules: JavaScript can fetch, compile, and instantiate Wasm modules.
• Calling Wasm Functions: Once a Wasm module is instantiated, JavaScript can call its exported functions.
• Calling JavaScript Functions from Wasm: Wasm modules can import and call JavaScript functions, allowing Wasm code to interact with browser APIs or JavaScript libraries.
• Shared Memory: For high-performance scenarios, Wasm and JavaScript can share memory, enabling efficient data exchange without costly copying.

This interoperability is key to Wasm's utility on the web.

How They Complement Each Other

Feature	JavaScript	WebAssembly
Primary Use	UI manipulation, event handling, general scripting	CPU-intensive tasks, performance-critical algorithms
Performance	Dynamically typed, JIT-compiled, generally slower for heavy computation	Statically typed, AOT-compiled, near-native speed
Language	JavaScript (and languages that transpile to JS)	C, C++, Rust, Go, AssemblyScript, etc.
Ecosystem	Vast, mature, rich with UI libraries/frameworks	Growing, leverages existing native libraries
Accessibility	Direct access to Web APIs (DOM, Fetch, etc.)	Accesses Web APIs via JavaScript interop

Practical Scenarios for Interoperation

1. Accelerating Bottlenecks:

   • Identify performance-critical sections of your JavaScript application (e.g., complex calculations, data processing).
   • Rewrite these sections in a language like Rust or C++, compile to Wasm.
   • Call the Wasm functions from your JavaScript code.
   • This is where tools providing advanced analytics platforms can see significant speedups.

2. Reusing Existing Code:

   • You have a valuable library written in C++ (e.g., a physics engine, an image codec).
   • Compile it to Wasm using Emscripten.
   • Use it in your web application via JavaScript bindings.

3. Building Rich Applications:

   • Use JavaScript and its frameworks (React, Vue, Angular) for the application's UI and overall structure.
   • Implement core logic or demanding modules in Wasm for performance.
   • For example, a web-based photo editor might use JavaScript for the UI and Wasm for image filtering algorithms.

Data Exchange

Passing complex data between JavaScript and Wasm requires careful consideration:

• Simple Numeric Types: Numbers can be passed directly as arguments and return values.
• Strings and Complex Objects: These often require serialization/deserialization or direct memory manipulation if using shared memory. Tools like wasm-bindgen (for Rust) help automate the generation of JavaScript glue code to handle these conversions.

The Future is Collaborative

WebAssembly and JavaScript are not competitors but collaborators. JavaScript remains the primary language of the web, excelling at dynamic tasks and UI interaction. WebAssembly provides a powerful way to augment JavaScript's capabilities, bringing near-native performance to the browser for tasks that demand it.

As both technologies evolve, their integration will likely become even smoother, enabling richer and more performant web experiences.

Our final post in this series will look at the future of WebAssembly. If you're exploring other modern technologies, you might find the discussion on cloud service models on our partner site interesting.