Are there any tags or elements that will definitely be there? How can I judge it through js?
If you have to use tags , see if these two count,
<!DOCTYPE html><meta name="viewport" content="initial-scale=1, maximum-scale=1, user-scalable=no">
<meta name="viewport" content="width=device-width"/>
<meta name="viewport" content="width=device-width"/>
I hope you will post more in the html5 section in the future. Of course, you can also post here