I am asked the following questions all the time by customers interested in making the jump to Office.js. Therefore, I am providing this FAQ as a primer which usually helps open the door to deeper discussions:
- What is Office.js exactly?
Office.js is a new way to develop customizations (or add-ins) for Office that are cross-platform. It is developed in JavaScript, runs from a webserver and loads into a content pane or task pane in the document or application.
- Cross-platform?
Yes. You can currently install or use an Office application (Word, Excel, PowerPoint and Outlook), on any of these platforms: Windows, Mac, iOS, Android (soon) or Web. There are some restrictions on what is supported and how much of the toolset is available per platform. See this article: Office Add-in host and platform availability
- Is Visual Basic for Macros (VBA), Visual Studio Tools for Office (VSTO), COM Add-ins or Macros going away then?
No. Office.js is just another development platform for Office. There are no plans to deprecate any of the other programmability options for Office. Office.js was designed with the Cloud First, Mobile first vision at Microsoft and expands customizations across multiple platforms. It can be thought of as add-ins that you write once, run anywhere.
- I have an existing COM add-in. Do I need convert it to Office.js?
No. Unless of course you want your add-in to work across multiple platforms. However, it is important to consider what your add-in is doing. The current application programming interfaces (APIs) for Office.js are more limited. While they are increasing in capability every day, they are still not on parity with COM, VBA or VSTO.
- Can I convert my add-in in Visual Studio?
No. This is because the new Office.js developer platform is completely new. There are no conversion tools. If you want to make the move to Office.js, you will likely need to start from scratch. However, if you have properly separated your backend logic from application interfaces, you might be able to reuse some of your existing code as a Web Service.
- How do determine if my existing COM add-in can be rewritten in Office.js?
This is harder to answer. The short answer is you try to create it in the new platform and see how much you can get to function. Longer answer, there are a couple of approaches:
- You rewrite the entire thing in the new platform and where some things do not translate or work the same, you change the requirements to meet the new platform restrictions, such as changing the workflow, number of features or expected results.
- You write as much as you can in the new platform and keep building on it as the platform continues to take shape. Whatever you cannot accomplish in Office.js you write as a VSTO add-in.
- You provide a more limited Office.js version for the non-Windows based platforms you support but still use your COM or VSTO add-in on Windows.
- How do I develop an Office.js add-in?
There are a number of editors you can use. These are web based so technically you can use any platform you want. I suggest using Visual Studio where you have templates the provide you with predefined templates for Word, Excel, PowerPoint and Outlook Web Add-ins. Also, the Publishing process is much simplified in my opinion with the Visual Studio tools.
- How do Office Web Add-ins work?
Office Web Add-ins are web pages. You publish the web pages to a web server and the entire solution will load and run from there. As part of developing the add-in, you will create an XML file called a manifest. The Manifest in simplest terms will define the name of your add-in, a unique ID for your add-in, its version, a description, any ribbon commands and the URL to the website. In Office you can then add the manifest and this will register the add-in in your Office application and load the ribbon buttons defined. When the user clicks the ribbons the manifest will tell Office what URL to load and then the add-in will appear in a content pane or task pane.
- What if I have more questions?
Please ask in the comments section and I will work to continue to expand this FAQ.