define(['events'], function (events) { function thresholdMonitor(elem, horizontal, lowerTolerance, upperTolerance) { var defaultTolerance = horizontal ? (screen.availWidth / 2) : (screen.availHeight / 2); lowerTolerance = lowerTolerance || defaultTolerance; upperTolerance = upperTolerance || defaultTolerance; var self = this; var upperTriggered = false; var lowerTriggered = false; var scrollSize; function getScrollSize() { if (!scrollSize) { scrollSize = horizontal ? (elem.scrollWidth - elem.clientWidth) : (elem.scrollHeight - elem.offsetHeight); } return scrollSize; } function onScroll(e) { if (lowerTriggered && upperTriggered) { return; } var position = horizontal ? elem.scrollLeft : elem.scrollTop; //console.log('onscroll: ' + position + '-' + getScrollSize()); // Detect upper threshold if (!upperTriggered && position < upperTolerance) { upperTriggered = true; events.trigger(self, 'upper-threshold'); } // Detect lower threshold if (!lowerTriggered && position >= (getScrollSize() - lowerTolerance)) { lowerTriggered = false; events.trigger(self, 'lower-threshold'); } } self.reset = function () { self.resetSize(); upperTriggered = false; lowerTriggered = false; }; self.resetSize = function () { scrollSize = null; }; self.enabled = function (enabled) { self.reset(); if (enabled) { elem.addEventListener('scroll', onScroll, true); } else { elem.removeEventListener('scroll', onScroll, true); } }; self.enabled(true); self.destroy = function () { self.enabled(false); }; } return thresholdMonitor; });