fix(adapter): fix progress event emitting; (#6518)

lib/helpers/throttle.js

@@ -1,5 +1,3 @@
-'use strict';
-
 /**
  * Throttle decorator
  * @param {Function} fn
@@ -8,28 +6,39 @@
  */
 function throttle(fn, freq) {
   let timestamp = 0;
-  const threshold = 1000 / freq;
-  let timer = null;
-  return function throttled() {
-    const force = this === true;
+  let threshold = 1000 / freq;
+  let lastArgs;
+  let timer;
 
+  const invoke = (args, now = Date.now()) => {
+    timestamp = now;
+    lastArgs = null;
+    if (timer) {
+      clearTimeout(timer);
+      timer = null;
+    }
+    fn.apply(null, args);
+  }
+
+  const throttled = (...args) => {
     const now = Date.now();
-    if (force || now - timestamp > threshold) {
-      if (timer) {
-        clearTimeout(timer);
-        timer = null;
+    const passed = now - timestamp;
+    if ( passed >= threshold) {
+      invoke(args, now);
+    } else {
+      lastArgs = args;
+      if (!timer) {
+        timer = setTimeout(() => {
+          timer = null;
+          invoke(lastArgs)
+        }, threshold - passed);
       }
-      timestamp = now;
-      return fn.apply(null, arguments);
     }
-    if (!timer) {
-      timer = setTimeout(() => {
-        timer = null;
-        timestamp = Date.now();
-        return fn.apply(null, arguments);
-      }, threshold - (now - timestamp));
-    }
-  };
+  }
+
+  const flush = () => lastArgs && invoke(lastArgs);
+
+  return [throttled, flush];
 }
 
 export default throttle;