Error Promise is undefined

Updated on Jan 28, 2026

Environment

Product	Progress® Telerik® Report Server
Operating System	Windows

Description

As of Telerik Reporting R2 2017, the Report Server and HTML5 Report Viewer require a browser supporting promises.The error indicates that the used browser does not support promises.

Please follow the HTML5 Viewer: Important Settings article which contains the requirements for promises.

Solution

Add a promise polyfill to the page, such as Polyfill.io.