WebAssembly (Wasm) is a binary instruction format that runs in web browsers at near-native speed, alongside JavaScript. It's typically compiled from languages like Rust, C++, or Go, and used for computationally heavy tasks (image/video processing, cryptography, physics simulation) where JavaScript's performance isn't sufficient.
WebAssembly is not a replacement for JavaScript — it's a companion. It's a low-level binary format that browsers can execute quickly because it's already close to machine code, unlike JavaScript, which the engine has to parse and JIT-compile from source text. Code written in Rust, C, C++, or Go can be compiled to a `.wasm` binary and loaded into a web page, called from JavaScript like any other module.
Wasm's performance advantage shows up in CPU-bound, computationally intensive work: image/PDF compression, video encoding, cryptographic operations, physics or numerical simulation. For typical UI logic, DOM manipulation, or API calls, Wasm provides no meaningful benefit and adds real complexity (a build toolchain, larger initial payload, JS-Wasm boundary overhead for data passing). The decision to use Wasm should follow a concrete performance bottleneck, not be a default choice.
No - they're complementary. JavaScript still handles DOM manipulation, event handling, and general app logic; Wasm is used selectively for the specific computationally-heavy pieces where it provides a measurable speed advantage.
Not directly - Wasm modules typically call back into JavaScript to interact with the DOM, since Wasm itself has no built-in concept of the browser's document object model.