Since the creation of the Office Add-ins framework, add-ins running in Office on Windows used a web viewer control that leveraged elements of Internet Explorer 11. While it was cutting edge at the time, web development standards have continued to evolve.

As we announced at Build 2019, to improve our support for web standards we are moving to an updated WebView control that is based on the current version of Microsoft Edge.

Beginning with Office 365 version 16.0.11629 and Windows 10 version 1903, Office Add-ins running on Office 365 for Windows will use a Microsoft Edge WebView as the runtime.

The Microsoft Edge WebView performs much better than Internet Explorer and features enhanced compliance with modern browser standards including support of the full set of HTML 5 and ECMAScript 2015+.

This change does not affect:

• Non-Windows Office versions, such as Office for Mac, iOS, Android, and Office Online. For information about which browser’s web viewer is used on these platforms and operating systems, see Web viewers used by Office Add-ins.
• Non-subscription versions of Office for Windows. These will continue to use Internet Explorer 11 as the web viewer.
• Office running on versions of Windows 10 lower than 1903. These will also continue to use Internet Explorer 11.
• Versions of Office lower than 16.0.11629. These will also continue to use Internet Explorer 11.

At Microsoft Build 2019, the Microsoft Edge team also announced new capabilities for the next version of Microsoft Edge , built on the Chromium open source project. We’re continuing to partner with the Microsoft Edge team to bring improved support for web standards to the Office add-ins platform.

General Availability of the new versions of Windows and Office 365

• Office 365, version 16.0.11629 will be the next Office 365 monthly update.
• Windows 10, version 1903 will be released in May, 2019.

Notes for Office Add-in Developers

• We recommend that you download the Microsoft Edge DevTools Preview for debugging.
• If you haven’t used JavaScript later than ES5 in the past because Internet Explorer did not support it, you may want to start using ECMAScript 2015 or later. For your add-in to still run on Windows and Office versions that do not use the Microsoft Edge viewer, you will need to either transpile your JavaScript to ES5 or use a polyfill.
• When loading an Office add-in from https://localhost or when using the Fiddler tool, you may see an error stating that a problem occurred while trying to reach your add-in. To fix this, follow either of these steps to add a local loopback exemption to “Desktop App Web Viewer”:
  • Open a command prompt as Administrator and run the following command: CheckNetIsolation LoopbackExempt -a -n=”microsoft.win32webviewhost_cw5n1h2txyewy” 
  • Using Fiddler: Select Tools > Win8 Loopback Exemptions and add an exemption to “Desktop App Web Viewer.”
• On Office builds before 1906 11727, a call of Office.Document.setSelectedDataAsync() will fail if all of the following conditions are met:
  • The data parameter is type TableData.
  • The TableData object has a header row, but no data rows.
  • The TableData object has more than one column.
• Please note that Service Workers are not supported on Microsoft Edge WebView for Office add-ins. Please see here for the latest supported features on the Edge WebView control. We are working hard to bring the new Chromium based Edge WebView2 to the Office add-ins platform, which we expect will support Service Workers.
• If you find a bug, report it as an issue at OfficeDev/office-js.