vertical scroll when zoomKey isn't triggered (#2197)

* Hide vertically hidden ranged items in groups that are not visible
* Add vertical scroll when zoom is inactive
* Fix review comments

lib/timeline/Core.js

@@ -157,9 +157,41 @@ Core.prototype._create = function (container) {
     if (me.isActive()) {
       me.emit('mousewheel', event);
     }
+
+    // prevent scrolling when zoomKey defined or activated
+    if (!me.options.zoomKey || event[me.options.zoomKey]) return
+
+    var delta = 0;
+    if (event.wheelDelta) { /* IE/Opera. */
+      delta = event.wheelDelta / 120;
+    } else if (event.detail) { /* Mozilla case. */
+      // In Mozilla, sign of delta is different than in IE.
+      // Also, delta is multiple of 3.
+      delta = -event.detail / 3;
+    }
+
+    var current = me.props.scrollTop;
+    var adjusted = current + delta * 120;
+    if (me.isActive()) {
+      me._setScrollTop(adjusted);
+      me._redraw();
+      me.emit('scroll', event);
+    }
+
+    // Prevent default actions caused by mouse wheel
+    // (else the page and timeline both scroll)
+    event.preventDefault();
+  }
+
+  if (this.dom.root.addEventListener) {
+    // IE9, Chrome, Safari, Opera
+    this.dom.root.addEventListener("mousewheel", onMouseWheel, false);
+    // Firefox
+    this.dom.root.addEventListener("DOMMouseScroll", onMouseWheel, false);
+  } else {
+    // IE 6/7/8
+    this.dom.root.attachEvent("onmousewheel", onMouseWheel);
   }
-  this.dom.root.addEventListener('mousewheel', onMouseWheel);
-  this.dom.root.addEventListener('DOMMouseScroll', onMouseWheel);
 
   // size properties of each of the panels
   this.props = {
@@ -222,7 +254,7 @@ Core.prototype.setOptions = function (options) {
     var fields = [
       'width', 'height', 'minHeight', 'maxHeight', 'autoResize',
       'start', 'end', 'clickToUse', 'dataAttributes', 'hiddenDates',
-      'locale', 'locales', 'moment', 'rtl'
+      'locale', 'locales', 'moment', 'rtl', 'zoomKey'
     ];
     util.selectiveExtend(fields, this.options, options);