Microsoft released the WebView2 browser control in October 2020. On Windows desktop, the future is WebView2 This is covered in Use the shared JavaScript runtime to improve the UI experience of your Office Add-in. Note: Office uses a JavaScript runtime for UI-less add-ins, such as custom functions in Excel and autorun add-ins in Outlook. In this post, we describe the latest changes in Office’s use of web runtimes as well as summarize the runtimes that we’ve used on various platforms in the past. You’re curious to learn how we are making this simpler (at least on Windows).You didn’t know that add-ins can run in eight different runtimes across various platforms.You’ve ever wondered why Office Add-ins need to support Internet Explorer even though Microsoft does not.For more information about which browser or control is used by the various platforms, see Browsers used by Office Add-ins. Since Office is a cross-platform suite, it uses different browsers, or webview controls, to run add-ins depending on the platform on which it is running.

A runtime can be encapsulated in a browser iFrame or an embeddable webview control on desktop clients. Think of a runtime as the execution environment for the add-in that’s a combination of a JavaScript engine and an HTML rendering control.

Office Add-ins require a runtime environment to execute.

Webview2 runtime download