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Promise is undefined error on loading the Report Viewer in the browser.


Product Progress® Telerik® Reporting
Version R2 2017 and later
Report Viewer HTML5 Report Viewers


As of  Telerik Reporting R2 2017, the HTML5 Viewer works only in browsers supporting promises. Trying to load a page with a HTML5 Report Viewer in it on a browser that does not support promises, will lead to the described error.

Error Message

"Error: 'Promise' is undefined".


The error appears in the browser when you load a page with the HTML5 Report Viewer on it.

The error indicates that the tested browser does not have support for promises.

Please check HTML5 Viewer: Important Settings and the requirements for promises.


If you do not have polyfill Javascript for promises on the page with the HTML5 Viewer, test to manually add a script tag with a link on the page with the viewer.

In our documentation, we suggest adding the polyfill file of The link with the content of the file can be previewed in a browser that does not have support for promises.


If you open the to retrieve the returned JS, the provided JS may not be correct since the endpoint has been opened by a browser that supports promises. Open the link with a browser that has no support for promises to ensure that the provided JS will work.

See Also

Promises - Browser compatibility

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