post canvas.js

async function upload(canvas,url) {
  let blob = await (new Promise(resolve => canvas.toBlob(resolve)));
  try {
    const response = await fetch(url, 
    {
      method:'POST',
      headers:{
        'Content-Type':'application/octet-stream'
      },
      body:blob
    });
  } catch(e) {console.log("fetch error: "+e.message)}
}