If you need to host a JavaScript SPA in SharePoint and display on external systems with <IFRAME>.    The below empty ASPX page can host a single Content Editor Web Part to effectively run JavaScript with light framing.  The page loads crazy fast too. 

I created it with SP Designer 2010 (https://www.spjeff.com/2014/05/08/get-design-view-back-on-sharepoint-2013-woohoo/) and WYSIWYG to embed a Web Part Zone and Content Editor above the blank ASPX default page.  

Screenshot

Code

<%@ Page Language="C#" inherits="Microsoft.SharePoint.WebPartPages.WebPartPage, Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>
<%@ Register tagprefix="WebPartPages" namespace="Microsoft.SharePoint.WebPartPages" assembly="Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>









None
Allows authors to enter rich text content.
true
2
Normal


true
true
true
true
true
true
true


Modeless
Default

Cannot import this Web Part.
/_layouts/15/images/mscontl.gif

true
00000000-0000-0000-0000-000000000000
g_73255e0f_a5df_4f4f_a551_8e11741b2e0d
/SitePages/Untitled.html