Dispatch custom scroll events with new updateScroll function

src/js/plugin/update-scroll.js

@@ -0,0 +1,85 @@
+/* Copyright (c) 2015 Hyunje Alex Jun and other contributors
+ * Licensed under the MIT License
+ */
+'use strict';
+
+var instances = require('./instances');
+
+var upEvent = document.createEvent('Event')
+  , downEvent = document.createEvent('Event')
+  , leftEvent = document.createEvent('Event')
+  , rightEvent = document.createEvent('Event')
+  , yEvent = document.createEvent('Event')
+  , xEvent = document.createEvent('Event')
+  , lastTop
+  , lastLeft;
+
+upEvent.initEvent('ps-scroll-up', true, true);
+downEvent.initEvent('ps-scroll-down', true, true);
+leftEvent.initEvent('ps-scroll-left', true, true);
+rightEvent.initEvent('ps-scroll-right', true, true);
+yEvent.initEvent('ps-scroll-y', true, true);
+xEvent.initEvent('ps-scroll-x', true, true);
+
+module.exports = function (element, axis, value) {
+  if (typeof element === 'undefined' ) {
+    throw 'You must provide an element to the update-scroll function';
+  }
+
+  if (typeof axis === 'undefined') {
+    throw 'You must provide an axis to the update-scroll function';
+  }
+
+  if (typeof value === 'undefined') {
+    throw 'You must provide a value to the update-scroll function'
+  }
+
+  if (value < 0) {
+    return; // don't allow negative scroll
+  }
+
+  var i = instances.get(element);
+
+  if (axis === 'top' && value > i.contentHeight - i.containerHeight) {
+    return; // don't allow scroll past container
+  }
+
+  if (axis === 'left' && value > i.contentWidth - i.containerWidth) {
+    return; // don't allow scroll past container
+  }
+
+  if (!lastTop) {
+    lastTop = element.scrollTop;
+  }
+
+  if (!lastLeft) {
+    lastLeft = element.scrollLeft;
+  }
+
+  if (axis === 'top' && value < lastTop) {
+    element.dispatchEvent(upEvent);
+  }
+
+  if (axis === 'top' && value > lastTop) {
+    element.dispatchEvent(downEvent);
+  }
+
+  if (axis === 'left' && value < lastLeft) {
+    element.dispatchEvent(leftEvent);
+  }
+
+  if (axis === 'left' && value > lastLeft) {
+    element.dispatchEvent(rightEvent);
+  }
+
+  if (axis === 'top') {
+    element.scrollTop = lastTop = value;
+    element.dispatchEvent(yEvent);
+  }
+
+  if (axis === 'left') {
+    element.scrollLeft = lastLeft = value;
+    element.dispatchEvent(xEvent);
+  }
+
+};