An internal error occurred during: “Requesting JavaScript AST from selection”

Sometime eclipse suddenly stops working by throwing following error
'Requesting Javascript AST from Selection' has encountered a problem. An internal error occured during "Requesting Javascript AST from selection"
and throws following error in the console, if you run eclipse through console.

java.lang.OutOfMemoryError: PermGen space 

Eclipse is not suitable for javascript validations. Sometimes it messes up with javascript and throws this error. You can disable javascript validation to get rid-off this error.

• Go to window-preferences, search for mark
• Select Javascript - editor - Mark Occurrences
• Uncheck Mark selected occurrences as shown below