Cache the window selector as 'viewport' in an attempt to improve performance.

(imported from commit 3e01382260938737fbee663f6a9e94ad495ef21e)

tools/jslint/check-all.js

@@ -45,7 +45,7 @@ var globals =
     + ' scroll_to_selected select_and_show_by_id'
     + ' selected_message selected_message_id'
     + ' at_top_of_viewport at_bottom_of_viewport'
-
+    + ' viewport'
     ;
 
 

zephyr/static/js/hotkey.js

@@ -46,7 +46,6 @@ function process_hotkey(code) {
             //
             // FIXME: this doesn't work for End because get_last_visible()
             // always returns a message.
-            var viewport = $(window);
             viewport.scrollTop($("#main_div").outerHeight(true));
         }
         return process_hotkey;

zephyr/static/js/ui.js

@@ -72,7 +72,6 @@ function mousemove() {
 }
 
 function resizehandler(e) {
-    var viewport = $(window);
     var sidebar = $("#sidebar");
     var sidebar_nav = $(".sidebar-nav");
     var composebox = $("#compose");
@@ -274,13 +273,11 @@ $(function () {
 
     $('#sidebar a[data-toggle="pill"]').on('show', function (e) {
         // Save the position of our old tab away, before we switch
-        var viewport = $(window);
         var old_tab = $(e.relatedTarget).attr('href');
         scroll_positions[old_tab] = viewport.scrollTop();
     });
     $('#sidebar a[data-toggle="pill"]').on('shown', function (e) {
         // Right after we show the new tab, restore its old scroll position
-        var viewport = $(window);
         var target_tab = $(e.target).attr('href');
         if (scroll_positions.hasOwnProperty(target_tab)) {
             viewport.scrollTop(scroll_positions[target_tab]);

zephyr/static/js/zephyr.js

@@ -4,6 +4,7 @@ var subject_dict = {};
 var people_hash = {};
 
 var selected_message_class = 'selected_message';
+var viewport = $(window);
 
 $(function () {
     var i;
@@ -69,14 +70,12 @@ var message_groups = {
 function above_view_threshold(message) {
     // Barnowl-style thresholds: the pointer is never above the
     // 1/5-mark.
-    var viewport = $(window);
     return message.offset().top < viewport.scrollTop() + viewport.height() / 5;
 }
 
 function below_view_threshold(message) {
     // Barnowl-style thresholds: the pointer is never below the
     // 4/5-mark.
-    var viewport = $(window);
     return message.offset().top + message.outerHeight(true) >
         viewport.scrollTop() + viewport.height() * 4 / 5;
 }
@@ -88,7 +87,6 @@ function recenter_view(message) {
 
     // If this logic changes, above_view_threshold andd
     // below_view_threshold must also change.
-    var viewport = $(window);
     if (above_view_threshold(message)) {
         viewport.scrollTop(selected_message.offset().top - viewport.height() / 2);
     } else if (below_view_threshold(message)) {
@@ -189,7 +187,6 @@ function update_selected_message(message) {
 }
 
 function select_message(next_message, scroll_to) {
-    var viewport = $(window);
 
     /* If the message exists but is hidden, try to find the next visible one. */
     if (next_message.length !== 0 && next_message.is(':hidden')) {
@@ -539,17 +536,15 @@ setInterval(function() {
 }, 5000);
 
 function at_top_of_viewport() {
-    return ($(window).scrollTop() === 0);
+    return (viewport.scrollTop() === 0);
 }
 
 function at_bottom_of_viewport() {
-    var viewport = $(window);
     return (viewport.scrollTop() + viewport.height() >= $("#main_div").outerHeight(true));
 }
 
 function keep_pointer_in_view() {
     var candidate;
-    var viewport = $(window);
     var next_message = get_message_row(selected_message_id);
 
     if (above_view_threshold(next_message) && (!at_top_of_viewport())) {