A WebAssembly compiler that fits in a tweet
One of the initial explorations that started this book was how small and simple a compile-to-WebAssembly language implemented in JavaScript could be. Our first “WebAssembly compiler in a tweet” was 269 bytes; since then, we’ve managed to whittle it down to a measly 192 bytes.
The final result is a compiler that takes an arithmetic expression — written in reverse polish notation — and compiles it down to a valid WebAssembly module. That module exports a single function which returns the result of the original arithmetic expression. Here it is:
But this is not just a clever trick — if you take the time to understand what this code does, you’ll learn a surprising amount about WebAssembly! In the rest of the post, we’ll explain how it all works by de-obfuscating the code one step at a time.
At a high level, what we’re doing is ‘parsing’ the expression in a very simple way, turning it into the appropriate Wasm bytecode, and then hand-crafting the bytes for a single-function module.
