feat(adapter): add fetch adapter; (#6371)

lib/helpers/progressEventReducer.js

@@ -0,0 +1,32 @@
+import speedometer from "./speedometer.js";
+import throttle from "./throttle.js";
+
+export default (listener, isDownloadStream, freq = 3) => {
+  let bytesNotified = 0;
+  const _speedometer = speedometer(50, 250);
+
+  return throttle(e => {
+    const loaded = e.loaded;
+    const total = e.lengthComputable ? e.total : undefined;
+    const progressBytes = loaded - bytesNotified;
+    const rate = _speedometer(progressBytes);
+    const inRange = loaded <= total;
+
+    bytesNotified = loaded;
+
+    const data = {
+      loaded,
+      total,
+      progress: total ? (loaded / total) : undefined,
+      bytes: progressBytes,
+      rate: rate ? rate : undefined,
+      estimated: rate && total && inRange ? (total - loaded) / rate : undefined,
+      event: e,
+      lengthComputable: total != null
+    };
+
+    data[isDownloadStream ? 'download' : 'upload'] = true;
+
+    listener(data);
+  }, freq);
+}