wasm_call.js

//retrieve image pixels (4 bytes per pixel: RBGA)
const data = imageData.data;
//copy to bytes to shared memory
mem.set(data);

//invoque 'fn'  Wasm filter. We need to inform of the image byte size
const byteSize = data.length;
instance.exports[fn](byteSize, ...args);

//copy the response from the shared memory into the canvas imageData
data.set(mem.slice(byteSize, 2*byteSize))
//update canvas
ctx.putImageData(imageData, 0, 0);