To make a wasm-based REPL for goal, you have to compile the package to wasm into a goal.wasm file located in the same directory, along index.html and style.css.

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

You also need to copy the wasm_exec.js support file corresponding to your Go version, as explained in Go Wiki: WebAssembly.

The resulting directory can then be served over HTTP.