diff --git a/demo/index.html b/demo/index.html
index abdfd0a3..794313f2 100644
--- a/demo/index.html
+++ b/demo/index.html
@@ -34,6 +34,9 @@
     </body>
     <script>
         var notfEl = document.getElementById('notf');
+        var num = 0;
+
+        // note: notification will close when clicked
         notfEl.addEventListener('click', function() {
             var title = document.getElementById('title').value;
             var body = document.getElementById('body').value;
@@ -41,26 +44,46 @@
             var shouldFlash = document.getElementById('flash').checked;
             var color = document.getElementById('color').value;
 
+            num++;
+
+            // notfs with same groupId will replace existing notf.
+            var groupId = (num % 2).toString();
             var notf = new SYM_API.Notification(title, {
-                body: body,
+                body: (body + ' num=' + num + ' groupId=' + groupId),
                 image: imageUrl,
                 flash: shouldFlash,
                 color: color || 'white',
                 data: {
                     hello: 'hello word'
-                }
+                },
+                groupId: groupId
             });
 
-            notf.addEventListener('click', function(event) {
+            notf.addEventListener('click', onclick);
+            function onclick(event) {
                 event.target.data.then(function(value) {
                     alert('notification clicked: ' + value.hello);
                 })
-            });
+            }
 
-            notf.addEventListener('close', function() {
+            notf.addEventListener('close', onclose);
+            function onclose() {
                 alert('notification closed');
-            });
+                removeEvents();
+            };
 
+            notf.addEventListener('error', onerror);
+            function onerror(event) {
+                alert('error=' + event.result);
+            };
+
+            // be sure to remove all events when closed, otherwise leaks
+            // will occur.
+            function removeEvents() {
+                notf.removeEventListener('click', onclick)
+                notf.removeEventListener('close', onclose)
+                notf.removeEventListener('error', onerror)
+            }
         });
 
         var badgeCount = 0;
diff --git a/js/notify/electron-notify-preload.js b/js/notify/electron-notify-preload.js
index 40998829..e56ae49d 100644
--- a/js/notify/electron-notify-preload.js
+++ b/js/notify/electron-notify-preload.js
@@ -54,11 +54,11 @@ function setContents(notificationObj) {
                 audio.play()
             }
         } catch (e) {
-            log('electron-notify: ERROR could not find sound file: ' + notificationObj.sound.replace('file://', ''), e, e.stack)
+            log('electron-notify: ERROR could not find sound file: ' + notificationObj.sound.replace('file://', ''), e, e.stack);
         }
     }
 
-    let notiDoc = window.document
+    let notiDoc = window.document;
 
     let container = notiDoc.getElementById('container');
 
@@ -78,34 +78,35 @@ function setContents(notificationObj) {
     }
 
     // Title
-    let titleDoc = notiDoc.getElementById('title')
-    titleDoc.innerHTML = notificationObj.title || ''
+    let titleDoc = notiDoc.getElementById('title');
+    titleDoc.innerHTML = notificationObj.title || '';
 
     // message
-    let messageDoc = notiDoc.getElementById('message')
-    messageDoc.innerHTML = notificationObj.text || ''
+    let messageDoc = notiDoc.getElementById('message');
+    messageDoc.innerHTML = notificationObj.text || '';
 
     // Image
-    let imageDoc = notiDoc.getElementById('image')
+    let imageDoc = notiDoc.getElementById('image');
     if (notificationObj.image) {
-        imageDoc.src = notificationObj.image
+        imageDoc.src = notificationObj.image;
     } else {
-        setStyleOnDomElement({ display: 'none'}, imageDoc)
+        setStyleOnDomElement({ display: 'none'}, imageDoc);
     }
 
     const winId = notificationObj.windowId;
 
-    // Close button
-    let closeButton = notiDoc.getElementById('close')
-    closeButton.addEventListener('click', function(clickEvent) {
+    let closeButton = notiDoc.getElementById('close');
+
+    // note: use onclick because we only want one handler, for case
+    // when content gets overwritten by notf with same groupId
+    closeButton.onclick = function(clickEvent) {
         clickEvent.stopPropagation()
         ipc.send('electron-notify-close', winId, notificationObj)
-    })
+    }
 
-    // URL
-    container.addEventListener('click', function() {
-        ipc.send('electron-notify-click', winId, notificationObj)
-    })
+    container.onclick = function() {
+        ipc.send('electron-notify-click', winId, notificationObj);
+    }
 }
 
 function setStyleOnDomElement(styleObj, domElement) {
diff --git a/js/notify/electron-notify.js b/js/notify/electron-notify.js
index c7ea342b..256723d0 100644
--- a/js/notify/electron-notify.js
+++ b/js/notify/electron-notify.js
@@ -229,20 +229,6 @@ function setupConfig() {
 
 
 function notify(notification) {
-    if (notificationQueue.length >= MAX_QUEUE_SIZE) {
-        var id = latestID;
-        incrementId();
-        if (typeof notification.onErrorFunc === 'function') {
-            setTimeout(function() {
-                notification.onErrorFunc({
-                    id: id,
-                    error: 'max notification queue size reached: ' + MAX_QUEUE_SIZE
-                });
-            }, 0);
-        }
-        return id;
-    }
-
     // Is it an object and only one argument?
     if (arguments.length === 1 && typeof notification === 'object') {
         let notf = Object.assign({}, notification);
@@ -265,6 +251,54 @@ function incrementId() {
 
 function showNotification(notificationObj) {
     return new Promise(function(resolve) {
+
+        if (notificationQueue.length >= MAX_QUEUE_SIZE) {
+            if (typeof notificationObj.onErrorFunc === 'function') {
+                setTimeout(function() {
+                    notificationObj.onErrorFunc({
+                        id: notificationObj.id,
+                        error: 'max notification queue size reached: ' + MAX_QUEUE_SIZE
+                    });
+                }, 0);
+            }
+            resolve();
+            return;
+        }
+
+        // check if group id provided.  should replace existing notification
+        // if has same grouping id.
+        let groupId = notificationObj.groupId;
+        if (groupId) {
+            // first check waiting items
+            for(let i = 0; i < notificationQueue.length; i++) {
+                if (groupId === notificationQueue[ i ].groupId) {
+                    notificationQueue[ i ] = notificationObj;
+                    resolve();
+                    return;
+                }
+            }
+
+            // next check items being shown
+            for(let i = 0; i < activeNotifications.length; i++) {
+                if (groupId === activeNotifications[ i ].groupId) {
+                    let notificationWindow = activeNotifications[ i ];
+
+                    // be sure to call close event for existing, so it gets
+                    // cleaned up.
+                    if (notificationWindow.electronNotifyOnCloseFunc) {
+                        notificationWindow.electronNotifyOnCloseFunc({
+                            event: 'close',
+                            id: notificationObj.id
+                        });
+                        delete notificationWindow.electronNotifyOnCloseFunc;
+                    }
+                    setNotificationContents(notificationWindow, notificationObj)
+                    resolve();
+                    return;
+                }
+            }
+        }
+
         // Can we show it?
         if (activeNotifications.length < config.maxVisibleNotifications) {
             // Get inactiveWindow or create new:
@@ -273,62 +307,76 @@ function showNotification(notificationObj) {
                 calcInsertPos()
                 setWindowPosition(notificationWindow, nextInsertPos.x, nextInsertPos.y)
 
-                // Add to activeNotifications
-                activeNotifications.push(notificationWindow)
+                let updatedNotfWindow = setNotificationContents(notificationWindow, notificationObj);
 
-                // Display time per notification basis.
-                let displayTime = notificationObj.displayTime ? notificationObj.displayTime : config.displayTime
+                activeNotifications.push(updatedNotfWindow);
 
-                // Set timeout to hide notification
-                let timeoutId
-                let closeFunc = buildCloseNotification(notificationWindow, notificationObj, function() {
-                    return timeoutId
-                })
-                let closeNotificationSafely = buildCloseNotificationSafely(closeFunc)
-                timeoutId = setTimeout(function() {
-                    closeNotificationSafely('timeout')
-                }, displayTime)
-
-                // Trigger onShowFunc if existent
-                if (notificationObj.onShowFunc) {
-                    notificationObj.onShowFunc({
-                        event: 'show',
-                        id: notificationObj.id,
-                        closeNotification: closeNotificationSafely
-                    })
-                }
-
-                var updatedNotificationWindow = notificationWindow;
-
-                // Save onClickFunc in notification window
-                if (notificationObj.onClickFunc) {
-                    updatedNotificationWindow.electronNotifyOnClickFunc = notificationObj.onClickFunc
-                } else {
-                    delete updatedNotificationWindow.electronNotifyOnClickFunc
-                }
-
-                if (notificationObj.onCloseFunc) {
-                    updatedNotificationWindow.electronNotifyOnCloseFunc = notificationObj.onCloseFunc
-                } else {
-                    delete updatedNotificationWindow.electronNotifyOnCloseFunc
-                }
-
-                const windowId = notificationWindow.id;
-                // Set contents, ...
-                updatedNotificationWindow.webContents.send('electron-notify-set-contents',
-                    Object.assign({ windowId: windowId}, notificationObj));
-                // Show window
-                updatedNotificationWindow.showInactive();
-                resolve(updatedNotificationWindow)
+                resolve(updatedNotfWindow);
             })
         } else {
             // Add to notificationQueue
-            notificationQueue.push(notificationObj)
-            resolve()
+            notificationQueue.push(notificationObj);
+            resolve();
         }
     })
 }
 
+function setNotificationContents(notfWindow, notfObj) {
+    // Display time per notification basis.
+    let displayTime = notfObj.displayTime ? notfObj.displayTime : config.displayTime;
+
+    if (notfWindow.displayTimer) {
+        clearTimeout(notfWindow.displayTimer);
+    }
+
+    // Set timeout to hide notification
+    let timeoutId;
+    let closeFunc = buildCloseNotification(notfWindow, notfObj, function() {
+        return timeoutId
+    });
+    let closeNotificationSafely = buildCloseNotificationSafely(closeFunc);
+    timeoutId = setTimeout(function() {
+        closeNotificationSafely('timeout');
+    }, displayTime);
+
+    var updatedNotificationWindow = notfWindow;
+
+    updatedNotificationWindow.displayTimer = timeoutId;
+
+    updatedNotificationWindow.groupId = notfObj.groupId;
+
+    // Trigger onShowFunc if existent
+    if (notfObj.onShowFunc) {
+        notfObj.onShowFunc({
+            event: 'show',
+            id: notfObj.id,
+            closeNotification: closeNotificationSafely
+        })
+    }
+
+    // Save onClickFunc in notification window
+    if (notfObj.onClickFunc) {
+        updatedNotificationWindow.electronNotifyOnClickFunc = notfObj.onClickFunc
+    } else {
+        delete updatedNotificationWindow.electronNotifyOnClickFunc;
+    }
+
+    if (notfObj.onCloseFunc) {
+        updatedNotificationWindow.electronNotifyOnCloseFunc = notfObj.onCloseFunc
+    } else {
+        delete updatedNotificationWindow.electronNotifyOnCloseFunc;
+    }
+
+    const windowId = notfWindow.id;
+    // Set contents, ...
+    updatedNotificationWindow.webContents.send('electron-notify-set-contents',
+        Object.assign({ windowId: windowId}, notfObj));
+    // Show window
+    updatedNotificationWindow.showInactive();
+
+    return updatedNotificationWindow;
+}
+
 // Close notification function
 function buildCloseNotification(notificationWindow, notificationObj, getTimeoutId) {
     return function(event) {
diff --git a/js/notify/notifyImpl.js b/js/notify/notifyImpl.js
index 3c9a0436..eac596a6 100644
--- a/js/notify/notifyImpl.js
+++ b/js/notify/notifyImpl.js
@@ -17,6 +17,7 @@ class Notify {
             image: options.image || options.icon,
             flash: options.flash,
             color: options.color,
+            groupId: options.groupId,
             onShowFunc: onShow.bind(this),
             onClickFunc: onClick.bind(this),
             onCloseFunc: onClose.bind(this),
@@ -35,6 +36,7 @@ class Notify {
         function onClick(arg) {
             if (arg.id === this._id) {
                 this.emitter.emit('click');
+                arg.closeNotification();
             }
         }
 
@@ -80,7 +82,7 @@ class Notify {
 
     removeEventListener(event, cb) {
         if (event && typeof cb === 'function') {
-            this.emitter.removeEventListener(event, cb);
+            this.emitter.removeListener(event, cb);
         }
     }
 
diff --git a/js/notify/notifyInterface.js b/js/notify/notifyInterface.js
index 006e8e83..afdad15f 100644
--- a/js/notify/notifyInterface.js
+++ b/js/notify/notifyInterface.js
@@ -24,6 +24,9 @@ class Notify {
      *  icon {string} url of image to show in notification
      *  flash {bool} true if notification should flash (default false)
      *  color {string} background color for notification
+     *  groupId {string} non-empty string to unique identify notf, if another
+     *    notification arrives with same groupId then it's content will
+     *    replace existing notification.
      *  data {object} arbitrary object to be stored with notification
      * }
      */
@@ -41,7 +44,8 @@ class Notify {
     static get permission() {}
 
     /**
-     * returns data object passed in via constructor options
+     * returns data object passed in via constructor options, return a
+     * promise that will be fullfilled with the data.
      */
     get data() {}