WebAssembly

Learn Go's WASM target.

WebAssembly

WebAssembly (WASM) is a portable binary format that runs at near-native speed in browsers and other runtimes. Go code can compile to WASM, so the same business logic runs on both the server and in the browser.

GOOS=js GOARCH=wasm go build -o main.wasm
cp "$(go env GOROOT)/lib/wasm/wasm_exec.js" .

On the browser side wasm_exec.js provides the bridge the Go runtime needs.

WASI

To run outside the browser (Wasmtime, Wasmer, serverless platforms) Go 1.21 added the GOOS=wasip1 target. WASI offers a standard interface to system functions such as files and clocks:

GOOS=wasip1 GOARCH=wasm go build -o app.wasm
wasmtime app.wasm

With Go 1.24 the //go:wasmexport directive can export Go functions to the host.

Exercise Portable logic

Write a pure function to be used both on the server and in WASM: kdv(fiyat float64) float64 adds 20% to the price. Print fmt.Printf("%.2f\n", kdv(100)).

Show example solution

package main

import "fmt"

func kdv(fiyat float64) float64 {
    return fiyat * 1.2
}

func main() {
    fmt.Printf("%.2f\n", kdv(100))
}

Test yourself

Why is a Go WASM binary usually several MB?
- WASM can't be compressed
- The browser adds it
- Debugging can't be turned off
- The Go runtime (GC, scheduler) is included in the binary
Show answer

The Go runtime (GC, scheduler) is included in the binary — Standard Go embeds the runtime in every binary; when a small WASM is needed TinyGo is preferred.

Target architecture

GOOS=js GOARCH=____ go build -o main.wasm

Show answer

GOOS=js GOARCH=wasm go build -o main.wasm

Target and environment

GOOS=js

Browser / Node.js
GOOS=wasip1

WASI runtimes
wasm_exec.js

JS bridge
//go:wasmexport

Export a function

Next lesson: GOOS=js

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