[3.x] Use set and clear debouncer upon completion. Fixes #5250.

lib/utils/debounce.js

@@ -36,6 +36,7 @@ export class Debouncer {
     this._timer = this._asyncModule.run(() => {
       this._timer = null;
       this._callback();
+      debouncerQueue.delete(this);
     });
   }
   /**
@@ -45,10 +46,19 @@ export class Debouncer {
    */
   cancel() {
     if (this.isActive()) {
-      this._asyncModule.cancel(/** @type {number} */(this._timer));
+      this._cancelAsync();
       this._timer = null;
+      debouncerQueue.delete(this);
     }
   }
+  /**
+   * Cancels a debouncer's async callback.
+   *
+   * @return {void}
+   */
+  _cancelAsync() {
+    this._asyncModule.cancel(/** @type {number} */(this._timer));
+  }
   /**
    * Flushes an active debouncer and returns a reference to itself.
    *
@@ -104,11 +114,47 @@ export class Debouncer {
    */
   static debounce(debouncer, asyncModule, callback) {
     if (debouncer instanceof Debouncer) {
-      debouncer.cancel();
+      // Cancel the async callback, but leave in debouncerQueue if it was
+      // enqueued, to maintain 1.x flush order
+      debouncer._cancelAsync();
     } else {
       debouncer = new Debouncer();
     }
     debouncer.setConfig(asyncModule, callback);
     return debouncer;
   }
 }
+
+let debouncerQueue = new Set();
+
+/**
+ * Adds a `Debouncer` to a list of globally flushable tasks.
+ *
+ * @param {!Debouncer} debouncer Debouncer to enqueue
+ * @return {void}
+ */
+export const enqueueDebouncer = function(debouncer) {
+  debouncerQueue.add(debouncer);
+};
+
+/**
+ * Flushes any enqueued debouncers
+ *
+ * @return {void}
+ */
+export const flushDebouncers = function() {
+  const didFlush = Boolean(debouncerQueue.size);
+  // If new debouncers are added while flushing, Set.forEach will ensure
+  // newly added ones are also flushed
+  debouncerQueue.forEach(debouncer => {
+    try {
+      debouncer.flush();
+    } catch(e) {
+      setTimeout(() => {
+        throw e;
+      });
+    }
+  });
+  debouncerQueue = new Set();
+  return didFlush;
+};

lib/utils/flush.js

@@ -11,32 +11,8 @@ import './boot.js';
 /* eslint-disable no-unused-vars */
 import { Debouncer } from '../utils/debounce.js';  // used in type annotations
 /* eslint-enable no-unused-vars */
-
-let debouncerQueue = [];
-
-/**
- * Adds a `Debouncer` to a list of globally flushable tasks.
- *
- * @param {!Debouncer} debouncer Debouncer to enqueue
- * @return {void}
- */
-export const enqueueDebouncer = function(debouncer) {
-  debouncerQueue.push(debouncer);
-};
-
-function flushDebouncers() {
-  const didFlush = Boolean(debouncerQueue.length);
-  while (debouncerQueue.length) {
-    try {
-      debouncerQueue.shift().flush();
-    } catch(e) {
-      setTimeout(() => {
-        throw e;
-      });
-    }
-  }
-  return didFlush;
-}
+import { flushDebouncers } from '../utils/debounce.js';  // used in type annotations
+export { enqueueDebouncer } from '../utils/debounce.js';  // used in type annotations
 
 /**
  * Forces several classes of asynchronously queued tasks to flush:

test/unit/debounce.html

@@ -33,6 +33,7 @@
 import { Polymer } from '../../polymer-legacy.js';
 import { Debouncer } from '../../lib/utils/debounce.js';
 import { microTask, timeOut, animationFrame, idlePeriod } from '../../lib/utils/async.js';
+import { enqueueDebouncer, flush } from '../../lib/utils/flush.js';
 Polymer({is: 'x-basic'});
 
 suite('debounce', function() {
@@ -209,6 +210,44 @@
     });
 
   });
+
+  suite('enqueueDebouncer & flush', function() {
+
+    const testEnqueue = (shouldFlush, done) => {
+      const actualOrder = [];
+      const enqueue = (type, {db, cb} = {}) => {
+        cb = cb || (() => actualOrder.push(cb));
+        db = Debouncer.debounce(db, type, cb);
+        enqueueDebouncer(db);
+        return {db, cb};
+      };
+      const db1 = enqueue(microTask);
+      const db2 = enqueue(microTask);
+      const db3 = enqueue(timeOut);
+      const db4 = enqueue(microTask);
+      enqueue(microTask, db2);
+      enqueue(microTask, db1);
+      if (shouldFlush) {
+        flush();
+        assert.deepEqual(actualOrder, [db1.cb, db2.cb, db3.cb, db4.cb]);
+        done();
+      } else {
+        timeOut.run(() => {
+          assert.deepEqual(actualOrder, [db4.cb, db2.cb, db1.cb, db3.cb]);
+          done();
+        });
+      }
+    };
+
+    test('non-flushed', function(done) {
+      testEnqueue(false, done);
+    });
+
+    test('flushed', function(done) {
+      testEnqueue(true, done);
+    });
+
+  });
 });
 </script>
 </body>