fix(post-bottom-bar): show and hide post bottom bar using the scrolli…

…ng delta

closes #498

source/_js/post-bottom-bar.js

@@ -12,8 +12,10 @@
     this.$postBottomBar = $('.post-bottom-bar');
     this.$postFooter = $('.post-actions-wrap');
     this.$header = $('#header');
-    this.delta = 1;
+    this.delta = 15;
     this.lastScrollTop = 0;
+    this.lastScrollDownPos = 0
+    this.lastScrollUpPos = 0
   };
 
   PostBottomBar.prototype = {
@@ -47,17 +49,26 @@
     swipePostBottomBar: function() {
       var scrollTop = $(window).scrollTop();
       var postFooterOffsetTop = this.$postFooter.offset().top;
-      // show bottom bar
-      // if the user scrolled upwards more than `delta`
-      // and `post-footer` div isn't visible
-      if (this.lastScrollTop > scrollTop &&
-        (postFooterOffsetTop + this.$postFooter.height() > scrollTop + $(window).height() ||
-        postFooterOffsetTop < scrollTop + this.$header.height())) {
-        this.$postBottomBar.slideDown();
+
+      // scrolling up
+      if (this.lastScrollTop > scrollTop) {
+        // show bottom bar
+        // if the user scrolled upwards more than `delta`
+        // and `post-footer` div isn't visible
+        if (Math.abs(this.lastScrollDownPos - scrollTop) > this.delta &&
+          (postFooterOffsetTop + this.$postFooter.height() > scrollTop + $(window).height() ||
+            postFooterOffsetTop < scrollTop + this.$header.height())) {
+          this.$postBottomBar.slideDown();
+          this.lastScrollUpPos = scrollTop
+        }
       }
-      else {
+
+      // scrolling down
+      if (scrollTop > this.lastScrollUpPos + this.delta) {
         this.$postBottomBar.slideUp();
+        this.lastScrollDownPos = scrollTop
       }
+
       this.lastScrollTop = scrollTop;
     }
   };