16 Patterns for Crossing the WebAssembly Boundary (And the One That Wants to Kill Them All)

WebAssembly is fast. We all know that by now. What almost nobody talks about is the hidden toll you pay every time you try to talk to it. The moment your JavaScript code needs to pass a measly string to a WASM module, or your WASM tries to touch a DOM node, you slam face-first into the boundary — a literal wall between two worlds with fundamentally opposed type systems, memory models, and execution paradigms. On one side, JS breathes UTF-16 strings, garbage-collected live objects, and async promises. On the other, WASM is spartan: it only understands numeric primitives like i32 or f64 , raw linear memory, and strictly synchronous execution. Crossing this boundary is never free. Every interaction has a price, and depending on the strategy you choose to pay it, that cost can range from mathematically negligible to a painful "why on earth did I bother compiling this to WASM?" What you're about to read is the definitive catalog of every known pattern for crossing this boundary, from the mo