All you have to do is open a JavaScript file. Euklas will parse the file automatically and will maybe show some errors in your file. It checks for missing function declarations and missing variable definitions.

The checks for existing errors are more sophisticated if you work with a file that contains copied & pasted code. You will find more information about this in the section on Copy & Paste. You should keep in mind that Euklas employs heuristic analysis to check for errors that are not correct in all cases. The section Ignore Errors talks in more details about this.