Office.js File

Your code must not call any Office.js APIs until this library is fully loaded
There are two ways that your code can ensure that the library is loaded.
Using Office.onReady to check to see if the Office.js library is fully loaded
Using Office.initialize to handle the initialize event that fires when the Office.js library is fully loaded and ready for user interaction.

Latest Production

This will refer to the latest production version

<script src="https://appsforoffice.microsoft.com/lib/1/hosted/Office.js" 
        type="text/javascript"> </script> 

Beta Testing

<script src="https://appsforoffice.microsoft.com/lib/beta/hosted/Office.js" 
        type="text/javascript"> </script> 

Local Copy

Alternatively you could refer to a local copy

<script src="../../Scripts/Office/1/Office.js" 
        type="text/javascript"> </script> 

Specific Versions

2015 September (1.1)
This tells it to always use the latest incremental release within version 1.

<script src="https://appsforoffice.microsoft.com/lib/1/hosted/Office.js" 
        type="text/javascript"> </script> 

2014 March (1.1)

<script src="https://appsforoffice.microsoft.com/lib/1.1/hosted/Office.js" 
        type="text/javascript"> </script> 

2012 August (1.0)

<script src="https://appsforoffice.microsoft.com/lib/1.0/hosted/Office.js" 
        type="text/javascript"> </script> 

JQuery

<script src="../../scripts/jquery-1.9.1.js" 
        type="text/javascript"> </script> 

<script src="../../scripts/jquery-2.1.4.js" 
        type="text/javascript"> </script> 

OfficeHelpers

This package is no longer being updated. more details

<link rel="stylesheet" 
      href="https://unpkg.com/@microsoft/office-js-helpers@1.0.2/dist/office.helpers.min.js"> 

unpkg.com

Used when trying out alpha or beta builds.

https://unpkg.com/@microsoft/office-js@1.1.10