Enhance detection of mobile browser scrolling #80

resources/assets/src/js/common/utils.js

@@ -62,6 +62,51 @@ function getQueryString(key, defaultValue) {
     }
 }
 
+/**
+ * Check if the `resize` event is fired by scrolling on a mobile browser
+ * whose address bar (e.g. Chrome) will hide automatically when scrolling.
+ *
+ * @return {Boolean}
+ */
+function isMobileBrowserScrolling() {
+    let currentWindowWidth  = $(window).width();
+    let currentWindowHeight = $(window).height();
+
+    if ($.cachedWindowWidth === undefined) {
+        $.cachedWindowWidth = currentWindowWidth;
+    }
+
+    if ($.cachedWindowHeight === undefined) {
+        $.cachedWindowHeight = currentWindowHeight;
+    }
+
+    let isWidthChanged  = (currentWindowWidth  !== $.cachedWindowWidth);
+    let isHeightChanged = (currentWindowHeight !== $.cachedWindowHeight);
+
+    // If the window width & height changes simultaneously, the resize can't be fired by scrolling.
+    if (isWidthChanged && isHeightChanged) {
+        return false;
+    }
+
+    // If only width was changed, it also can't be.
+    if (isWidthChanged) {
+        return false;
+    }
+
+    // If width didn't change but height changed ?
+    if (isHeightChanged) {
+        let last = $.lastWindowHeight;
+        $.lastWindowHeight = currentWindowHeight;
+
+        if (last === undefined || currentWindowHeight == last) {
+            return true;
+        }
+    }
+
+    // If both width & height did not change
+    return false;
+}
+
 /**
  * Return a debounced function
  *
@@ -101,5 +146,6 @@ if (typeof require !== 'undefined' && typeof module !== 'undefined') {
         isEmpty,
         debounce,
         getQueryString,
+        isMobileBrowserScrolling,
     };
 }

resources/views/index.tpl

@@ -128,8 +128,6 @@
 
     <script type="text/javascript">
 
-        var cachedWindowWidth = $(window).width();
-
         function changeWrapperHeight() {
             var btn = $('p a.button');
             var bottom = btn.offset().top + btn.height() + 80;
@@ -153,9 +151,7 @@
             .scroll(changeHeaderTransparency)
             .ready(changeWrapperHeight)
             .resize(function () {
-                if ($(window).width() !== cachedWindowWidth) {
+                isMobileBrowserScrolling() ? null : changeWrapperHeight();
-                    changeWrapperHeight();
-                }
             });
     </script>
 </body>