Here is my experience with the applications based on Extjs in UI with Java as server side language. I am a big supporter of open source technologies/products.
I so far I have used Eclipse, Netbeans, Webstorm and notepad++ with some added plugins.
And I feel Netbeans is best in terms of Syntax highlighting and formating. It recognizes missing commas, global variables, duplicate keys for object literals in a very impressive way.
Almost similar things can be achieved by adding some pligins like Spket in eclipse too, but it asks for licence when you go for advance level of settings.
If you are not so much concern about an integrated environment with web server then Web storm is best in all the aspects, but the biggest drawback of it is, "Its paid". ( Even if it asks for 1000 Rs ).