TelerikBlazor.getWindowWidth Was Undefined

Updated on Oct 8, 2026

Environment

Product	UI for Blazor
Version	15.0.0 and above

Description

An issue can occur when upgrading Telerik UI for Blazor from version 14- to 15+. The problem manifests as a JavaScript error at runtime that is similar to:

Unhandled exception rendering component: Could not find 'TelerikBlazor.getWindowWidth' ('getWindowWidth' was undefined).

or

Microsoft.JSInterop.JSException: The value 'TelerikBlazor.getWindowWidth' is not a function.

Cause

getWindowWidth is a new JavaScript function in telerik-blazor.js in Telerik UI for Blazor version 15.0.0. If there is an error about it missing, this means that the app is loading an outdated version of the telerik-blazor.js file, due to:

• Browser cache
• Incorrect CDN file URL
• Outdated local file in wwwroot

Solution

Depending on the above cause:

• Clear the browser cache and see how to avoid browser caching issues during component version upgrades.
• Replace the CDN file URL.
• Replace the local file in wwwroot.

See Also

• Prevent Browser Caching of Telerik CSS and JavaScript Files
• Troubleshoot JavaScript Errors
• Telerik UI for Blazor Upgrade Tutorial