Have front page load minimal JS necessary.

By creating a small file with only what is needed (focus, js flagging),
we can drop loading jQuery and all the application JavaScript on the
front page, prefetching them instead.

5 files changed, 31 insertions, 4 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a5224b3fd..9f1d99695 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@
     - Front end improvements:
         - Remove unneeded 2x PNG fallback images.
         - Individual cobrands can disable social login #1890
+        - Improve performance of various pages, especially front. #1903
     - Bugfixes
         - Shortlist menu item always remains a link #1855
         - Fix encoded entities in RSS output. #1859
diff --git a/templates/web/base/common_header_tags.html b/templates/web/base/common_header_tags.html
index 1dad1cfa0..f65f1e336 100644
--- a/templates/web/base/common_header_tags.html
+++ b/templates/web/base/common_header_tags.html
@@ -36,7 +36,12 @@
 
 [% IF bodyclass.match('frontpage') %]
     <link rel="prefetch" href="[% version('/js/validation_rules.js') %]">
+  [%~ IF NOT c.user_exists OR NOT (c.user.from_body OR c.user.is_superuser) %]
+    <link rel="prefetch" href="[% version('/jslib/jquery-1.7.2.min.js') %]">
+  [%~ END %]
+    <link rel="prefetch" href="[% version('/js/jquery.multi-select.js') %]">
     <link rel="prefetch" href="[% version('/vendor/jquery.validate.min.js') %]">
+    <link rel="prefetch" href="[% version('/cobrands/fixmystreet/fixmystreet.js') %]">
 [% END %]
 [% IF NOT bodyclass.match('mappage') %]
     [% FOR script IN map_js %]
diff --git a/templates/web/base/common_scripts.html b/templates/web/base/common_scripts.html
index b04404f06..c6225e8fa 100644
--- a/templates/web/base/common_scripts.html
+++ b/templates/web/base/common_scripts.html
@@ -7,15 +7,14 @@ scripts = [];
 
 scripts.push(
     start _ "/js/translation_strings." _ lang_code _ ".js?" _ Math.int( date.now / 3600 ),
-    version('/jslib/jquery-1.7.2.min.js'),
-    version('/js/jquery.multi-select.js'),
-    version('/cobrands/fixmystreet/fixmystreet.js'),
 );
 
+SET jquery_loaded = 0;
 SET geolocation_loaded = 0;
 IF bodyclass.match('frontpage');
     SET geolocation_loaded = 1;
     scripts.push(
+        version('/js/front.js'),
         version('/js/geolocation.js'),
     );
 ELSIF bodyclass.match('alertpage');
@@ -24,9 +23,13 @@ ELSIF bodyclass.match('alertpage');
         version('/js/geolocation.js'),
     );
 ELSE;
+    SET jquery_loaded = 1;
     scripts.push(
         version('/js/validation_rules.js'),
+        version('/jslib/jquery-1.7.2.min.js'),
+        version('/js/jquery.multi-select.js'),
         version('/vendor/jquery.validate.min.js'),
+        version('/cobrands/fixmystreet/fixmystreet.js'),
     );
 END;
 
@@ -40,6 +43,11 @@ IF c.user_exists AND (c.user.from_body OR c.user.is_superuser);
             version('/js/geolocation.js'),
         );
     END;
+    IF NOT jquery_loaded;
+        scripts.push(
+            version('/jslib/jquery-1.7.2.min.js'),
+        );
+    END;
     scripts.push(
         version('/cobrands/fixmystreet/staff.js')
     );
diff --git a/templates/web/fixmystreet.com/footer_extra_js.html b/templates/web/fixmystreet.com/footer_extra_js.html
index 2b024bfa4..cb1b78743 100644
--- a/templates/web/fixmystreet.com/footer_extra_js.html
+++ b/templates/web/fixmystreet.com/footer_extra_js.html
@@ -8,7 +8,7 @@ IF bodyclass.match('frontpage');
     scripts.push(
         version('/cobrands/fixmystreet.com/front.js'),
     );
-ELSE;
+ELSIF NOT bodyclass.match('alertpage');
     scripts.push(
         version('/cobrands/fixmystreet.com/js.js'),
     );
diff --git a/web/js/front.js b/web/js/front.js
new file mode 100644
index 000000000..d2c814490
--- /dev/null
+++ b/web/js/front.js
@@ -0,0 +1,13 @@
+document.getElementById('pc').focus();
+
+(function(){
+    var around_forms = document.querySelectorAll('form[action*="around"]');
+    for (var i=0; i<around_forms.length; i++) {
+        var form = around_forms[i];
+        var el = document.createElement('input');
+        el.type = 'hidden';
+        el.name = 'js';
+        el.value = 1;
+        form.insertBefore(el, form.firstChild);
+    }
+})();