To view JScript Errors as Errors in Error List window enable below option from Options dialog of Visual Studio
– Launch Options dialog by clicking on Tool à Options menu
– Expand Text Editor à HTML à Validation
– Clear Show errors “as warnings (JScript)” check box
This has been added after VS 2008 Beta2 after considering customer feedback. In Visual Studio 2005 and Visual Web Developer Express 2005 all markup and CSS validation related issues such as unsupported tags and attributes are shown as errors in Error List. Few like it since validation errors encourage standard compliance while few didn’t want validation errors to show up in Error list as these errors are browser errors. The same applies for JScript errors in VS 2008. This has been addressed by adding above option in the final version of Visual Studio 2008.