Add:Lazy bookshelf

objects/TouchEvent.js

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+// SOURCE: https://stackoverflow.com/a/69617795/7431543
+export default class TouchEvent {
+    static SWPIE_THRESHOLD = 50 // Minumum difference in pixels at which a swipe gesture is detected
+
+    static SWIPE_LEFT = 1
+    static SWIPE_RIGHT = 2
+    static SWIPE_UP = 3
+    static SWIPE_DOWN = 4
+
+    constructor(startEvent, endEvent) {
+        this.startEvent = startEvent
+        this.endEvent = endEvent || null
+    }
+
+    isSwipeLeft() {
+        return this.getSwipeDirection() == TouchEvent.SWIPE_LEFT
+    }
+
+    isSwipeRight() {
+        return this.getSwipeDirection() == TouchEvent.SWIPE_RIGHT
+    }
+
+    isSwipeUp() {
+        return this.getSwipeDirection() == TouchEvent.SWIPE_UP
+    }
+
+    isSwipeDown() {
+        return this.getSwipeDirection() == TouchEvent.SWIPE_DOWN
+    }
+
+    getSwipeDirection() {
+        let start = this.startEvent.changedTouches[0]
+        let end = this.endEvent.changedTouches[0]
+
+        if (!start || !end) {
+            return null
+        }
+
+        let horizontalDifference = start.screenX - end.screenX
+        let verticalDifference = start.screenY - end.screenY
+
+        // Horizontal difference dominates
+        if (Math.abs(horizontalDifference) > Math.abs(verticalDifference)) {
+            if (horizontalDifference >= TouchEvent.SWPIE_THRESHOLD) {
+                return TouchEvent.SWIPE_LEFT
+            } else if (horizontalDifference <= -TouchEvent.SWPIE_THRESHOLD) {
+                return TouchEvent.SWIPE_RIGHT
+            }
+
+            // Verical or no difference dominates
+        } else {
+            if (verticalDifference >= TouchEvent.SWPIE_THRESHOLD) {
+                return TouchEvent.SWIPE_UP
+            } else if (verticalDifference <= -TouchEvent.SWPIE_THRESHOLD) {
+                return TouchEvent.SWIPE_DOWN
+            }
+        }
+
+        return null
+    }
+
+    setEndEvent(endEvent) {
+        this.endEvent = endEvent
+    }
+}