From ccd2433345abb4652f9fcfca9fb8027a66043f3a Mon Sep 17 00:00:00 2001
From: Jessica McKellar <jesstess@humbughq.com>
Date: Fri, 2 Aug 2013 17:56:28 -0400
Subject: [PATCH] Let the browser scroll happen before our scrolling on a
 (re)load.

On a page load or reload, the browser will, at an idle time, scroll to
the top of the page. We can't intercept this browser-induced scroll,
so to make sure it doesn't in interfere with our scrolling to the
correct place in your message feed, we let the browser scroll happen
before the work we do on page load.

(imported from commit f5f441ab90bcdb8404e05caea3c6da81a3a6fc1e)
---
 static/js/ui.js    | 10 ++++++----
 static/js/zulip.js | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/static/js/ui.js b/static/js/ui.js
index 6f963037ad..fdcc6ed493 100644
--- a/static/js/ui.js
+++ b/static/js/ui.js
@@ -1401,10 +1401,12 @@ function scroll_finish() {
     scroll_timer = setTimeout(scroll_finished, 100);
 }
 
-$(window).scroll($.throttle(50, function (e) {
-    process_visible_unread_messages();
-    scroll_finish();
-}));
+exports.register_scroll_handler = function () {
+    $(window).scroll($.throttle(50, function (e) {
+        process_visible_unread_messages();
+        scroll_finish();
+    }));
+};
 
 var presence_descriptions = {
     active: 'is active',
diff --git a/static/js/zulip.js b/static/js/zulip.js
index ffaf5567d6..75073662fb 100644
--- a/static/js/zulip.js
+++ b/static/js/zulip.js
@@ -39,6 +39,8 @@ var pointer_update_in_flight = false;
 
 var events_stored_during_tutorial = [];
 
+var waiting_on_browser_scroll = true;
+
 function add_person(person) {
     page_params.people_list.push(person);
     people_dict[person.email] = person;
@@ -1051,6 +1053,13 @@ function process_result(messages, opts) {
 }
 
 function get_old_messages_success(data, opts) {
+    if (waiting_on_browser_scroll) {
+        setTimeout(function () {
+            get_old_messages_success(data, opts);
+        }, 25);
+        return;
+    }
+
     if (opts.msg_list.narrowed && opts.msg_list !== current_msg_list) {
         // We unnarrowed before receiving new messages so
         // don't bother processing the newly arrived messages.
@@ -1315,6 +1324,35 @@ function main() {
     }
 }
 
+function install_main_scroll_handler() {
+    waiting_on_browser_scroll = false;
+    // Unregister this special un-throttled scroll handler.
+    $(window).unbind("scroll");
+    // Register the normal throttled scroll handler.
+    ui.register_scroll_handler();
+}
+
 $(function () {
+    // On a page load or reload, the browser will, at an idle time, scroll to
+    // the top of the page. We can't intercept this browser-induced scroll, so
+    // to make sure it doesn't in interfere with our scrolling to the correct
+    // place in your message feed, we let the browser scroll happen first.
+
+    // After some time, if we haven't seen the browser scroll, give up
+    // and call main.
+    var browser_scroll_timer = setTimeout(function () {
+        install_main_scroll_handler();
+    }, 500);
+
+    (window).scroll(function () {
+        if (viewport.scrollTop() < viewport.height()) {
+            // This is the browser-induced scroll to the top of the
+            // page that we were waiting for. It only happens once,
+            // so stop waiting and call main.
+            install_main_scroll_handler();
+            clearTimeout(browser_scroll_timer);
+        }
+    });
+
     main();
 });