Request body writing as a stream

gistfile1.js

var req = new Request('https://example.com' { bodyAsWriter: true });

// throws because writer is not set yet
req.bodyWriter.write(/*...*/);

// fetch calls setWriter
fetch(req).then(/*...*/);

req.bodyWriter.write(/*...*/)

var req2 = new Request('https://example.com' { body: arrayBuffer, bodyAsWriter: true });

// fetch calls setWriter and body.PipeTo(bodyWriter)
fetch(req2).then(/*...*/);

// wait for constructor body to be complete and then write a trailer
req2.body.closed.then(function() {
  req.bodyWriter.write(/*...*/);
});