Hook for adding JS to all admin pages

Like insert_editor_js but not just for edit pages.

docs/reference/hooks.rst

@@ -321,6 +321,26 @@ Add additional CSS files or snippets to all admin pages.
       )
 
 
+.. _insert_global_admin_js:
+
+``insert_global_admin_js``
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+  Add additional JavaScript files or code snippets to all admin pages.
+
+  .. code-block:: python
+
+    from django.utils.html import format_html
+
+    from wagtail.wagtailcore import hooks
+
+    @hooks.register('insert_global_admin_js')
+    def global_admin_js():
+      return format_html('<script src="' \
+      + 'https://cdnjs.cloudflare.com/ajax/libs/three.js/r74/three.js' \
+      + '"></script>')
+
+
 Editor workflow
 ---------------
 

wagtail/wagtailadmin/templates/wagtailadmin/admin_base.html

@@ -25,6 +25,7 @@
     <script src="{% static 'wagtailadmin/js/vendor/jquery.dlmenu.js' %}"></script>
     <script src="{% static 'wagtailadmin/js/vendor/tag-it.js' %}"></script>
     <script src="{% static 'wagtailadmin/js/core.js' %}"></script>
+    {% hook_output 'insert_global_admin_js' %}
 
     {% main_nav_js %}