Cannot read properties of null (reading addEventListener)
Environment
| Product | UI for Blazor |
| Blazor application type | WebAssembly |
Description
JSInterop (JavaScript) error in the browser devtools console:
Cannot read properties of null (reading 'addEventListener')
Steps to Reproduce
The error can occur in WebAssembly (WASM) projects after updating UI for Blazor to a new version.
Error Message
Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100]
Unhandled exception rendering component: Cannot read properties of null (reading 'addEventListener')
TypeError: Cannot read properties of null (reading 'addEventListener')
Microsoft.JSInterop.JSException: Cannot read properties of null (reading 'addEventListener')
TypeError: Cannot read properties of null (reading 'addEventListener')
Possible Cause
The error indicates that the app is still using the old version of our telerik-blazor.js file.
Solution
To resolve the error:
- (if using CDN) Update the
telerik-blazor.jsfile URL to the correct version. - (if using static assets) Clear the browser cache and add a cache buster for the Telerik assets.
- (if using a local JS file) Replace the
telerik-blazor.jsfile with the new version.
Notes
The Blazor framework should normally take care of caching issues with static assets, but they might still occur sometimes.