Add zoomFriction option

docs/src/OptionsPage.js

@@ -832,6 +832,16 @@ class OptionsPage extends React.Component {
           </td>
         </tr>
 
+        <tr>
+          <td>zoomFriction</td>
+          <td>number</td>
+          <td><code>5</code></td>
+          <td>
+            Specifies how strong the zooming is for each scroll tick. Higher zooming friction will slow
+            zooming speed.
+          </td>
+        </tr>
+
         <tr>
           <td>zoomKey</td>
           <td>String</td>

examples/basicUsage.html

@@ -9,7 +9,7 @@
     }
   </style>
 
-  <script src="../dist/timeline.js"></script>
+  <script src="../dist/timeline.min.js"></script>
   <link href="../dist/timeline.min.css" rel="stylesheet" type="text/css" />
 
 </head>

lib/timeline/Core.js

@@ -387,7 +387,7 @@ class Core {
       const fields = [
         'width', 'height', 'minHeight', 'maxHeight', 'autoResize',
         'start', 'end', 'clickToUse', 'dataAttributes', 'hiddenDates',
-        'locale', 'locales', 'moment', 'rtl', 'zoomKey', 'horizontalScroll', 'verticalScroll'
+        'locale', 'locales', 'moment', 'rtl', 'zoomKey', 'zoomFriction', 'horizontalScroll', 'verticalScroll'
       ];
       util.selectiveExtend(fields, this.options, options); 
 

lib/timeline/Range.js

@@ -101,7 +101,7 @@ export default class Range extends Component {
       // copy the options that we know
       const fields = [
         'animation', 'direction', 'min', 'max', 'zoomMin', 'zoomMax', 'moveable', 'zoomable',
-        'moment', 'activate', 'hiddenDates', 'zoomKey', 'rtl', 'showCurrentTime', 'rollingMode', 'horizontalScroll'
+        'moment', 'activate', 'hiddenDates', 'zoomKey', 'zoomFriction', 'rtl', 'showCurrentTime', 'rollingMode', 'horizontalScroll'
       ];
       util.selectiveExtend(fields, this.options, options);
 
@@ -635,12 +635,14 @@ export default class Range extends Component {
 
       // adjust a negative delta such that zooming in with delta 0.1
       // equals zooming out with a delta -0.1
+
+      const zoomFriction = this.options.zoomFriction || 5;
       let scale;
       if (delta < 0) {
-        scale = 1 - (delta / 5);
+        scale = 1 - (delta / zoomFriction);
       }
       else {
-        scale = 1 / (1 + (delta / 5)) ;
+        scale = 1 / (1 + (delta / zoomFriction)) ;
       }
 
       // calculate center, the date to zoom around

lib/timeline/optionsTimeline.js

@@ -178,6 +178,7 @@ let allOptions = {
   width: {string, number},
   zoomable: { 'boolean': bool},
   zoomKey: {string: ['ctrlKey', 'altKey', 'metaKey', '']},
+  zoomFriction: {number},
   zoomMax: {number},
   zoomMin: {number},