Office VSTO Add-ins vs Office Add-ins using Office JS API

Question

Recently Microsoft introduced the Office Add-ins architecture which allows for developing add-ins hosted remotely and run within IFrames inside office. I have read a lot trying to understand whether this architecture is meant as a replacement for VSTO or do they have separate use-cases. VS 2015 has templates for both.

In my specific case, I want to develop an add-in that extends Excel 2016 with custom import functionality (e.g. custom CSVs, TSV, or even XLSX). I can't tell which type of project I should go with.

Answer 1

Given the amount of legacy applications developed as COM and VSTO add-ins I find it hard to believe Microsoft would drop support within the next 10 years.

For me the most important differentiators of one approach vs. the other are:

COM/VSTO Office add-ins

• Access to complete object model
• Local machine interaction, e.g. file system
• Available on Windows since Office 2007

JavaScript Office Add-ins

• Portable between Windows, OS X, iOS etc. (not complete everywhere yet though)
• Easy integration with online services
• Easy distribution, no need to worry about installers

In your case I'd ask myself these questions:

• Will there be a need to support other platforms besides Windows in the future? > JavaScript API
• Are the requirements covered by the current JavaScript API implementation?

Answer 2

I've found that VSTO isn't 100% implemented either. I've given up developing VSTO for Project, got hit by too many issues. Instead I've developed everything in VBA and have perfected some neat ways to install, distribute and update VBA macros.