Prevent autofocus when page has scrolled

If users scroll a page with an autofocus component
on so it is off-screen it seems safe to assume
they won't want it focused if they return to it.

This prevents that happening.

This adds a data-attribute flag to allow this
behaviour to be overridden.

We have some situations where the assumption here
isn't appropriate, for example on pages where the
component with autofocus is in a sticky element.
This means it will appear offscreen when the page
loads but, when its parent becomes sticky, will be
visible again.

app/assets/javascripts/autofocus.js

@@ -2,9 +2,14 @@
   "use strict";
 
   Modules.Autofocus = function() {
-    this.start = function(component) {
+    this.start = function($component) {
+      var forceFocus = $component.data('forceFocus');
 
-      $('input, textarea, select', component).eq(0).trigger('focus');
+      // if the page loads with a scroll position, we can't assume the item to focus onload
+      // is still where users intend to start
+      if (($(window).scrollTop() > 0) && !forceFocus) { return; }
+
+      $('input, textarea, select', $component).eq(0).trigger('focus');
 
     };
   };

app/templates/views/send-test.html

@@ -16,7 +16,8 @@
 
   {% call form_wrapper(
     class='js-stick-at-top-when-scrolling send-one-off-form' if template.template_type != 'sms' else 'send-one-off-form',
-    module="autofocus"
+    module="autofocus",
+    data_kwargs={'forceFocus': True}
   ) %}
     <div class="grid-row">
       <div class="column-two-thirds {% if form.placeholder_value.label.text == 'phone number' %}extra-tracking{% endif %}">