General use body-logger to use with browser fetch - riffing on https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream/getReader

logReadableStream.js

/*
  fetch('http://example.com')
    .then(res => res.ok ? logReadableStream(res.body) : Promise.reject(`Status: ${res.status}`))
    .catch(console.log)
*/
let logReadableStream = function (stream) {
  const reader = stream.getReader();
  let bytesReceived = 0;
  let result = new Uint8Array(0);

  const readableStreamLogger = function ({ done, value }) {
    if (done) {
      console.log('Stream complete: ' + new TextDecoder('utf-8').decode(result));
      return;
    }

    bytesReceived += value.length;
    console.log('Received ' + bytesReceived + ' bytes so far');
    
    // value for fetch streams is a Uint8Array
    const nextResult = new Uint8Array(result.length + value.length)
    nextResult.set(result);
    nextResult.set(value);
    result = nextResult;

    return reader.read().then(readableStreamLogger);
  };

  return reader.read().then(readableStreamLogger);
}