var toolbar = Polymer.dom(document).querySelector('#main-toolbar')
var toolbar = document.querySelector('#main-toolbar');
<paper-toolbar id="main-toolbar">
1）当document.querySelector成为影子dom元素时，为什么paper-toolbar可以使用querySelector？或另一种方式来说明......为什么它适用于本地dom中的元素？
2）因为这两个Traceback (most recent call last):
File "manage.py", line 10, in <module>
execute_from_command_line(sys.argv)
File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/django/core/management/__init__.py", line 351, in execute_from_command_line
utility.execute()
File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/django/core/management/__init__.py", line 343, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/django/core/management/__init__.py", line 177, in fetch_command
commands = get_commands()
File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/django/core/management/__init__.py", line 72, in get_commands
for app_config in reversed(list(apps.get_app_configs())):
File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/django/apps/registry.py", line 137, in get_app_configs
self.check_apps_ready()
File "/Library/Frameworks/Python.framework/Vers`enter code here`ions/3.5/lib/python3.5/site-packages/django/apps/registry.py", line 124, in check_apps_ready
raise AppRegistryNotReady("Apps aren't loaded yet.")
django.core.exceptions.AppRegistryNotReady: Apps aren't loaded yet.
都有效，哪个更好用？
答案 0 :(得分：1)
工具栏不在聚合物元素内。 你可以使用document.querySelector（'＃main-toolbar'）; 这里不需要使用Polymer API（聚合物元素是HTML元素）。 聚合物API可用于访问阴影/阴影DOM（聚合物元素内部）。