Single Page Applications offer great performance and user experience benefits when building web applications. By leveraging capabilities of modern browsers you can dynamically load the resources necessary for the particular part of the application with which the user is interacting at the given moment.
As long as your Single Page Application is tied to a specific Office 365 tenant, you can fully benefit of CORS and have your application work completely using client-side code. For multi-tenant applications things are a bit more complicated.
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