JSView is an app plus a Safari extension that makes it easy to do one key web developer task: view the JavaScript & CSS source of any web page, with beautiful and customisable syntax highlighting.
Just browse the web in Safari as you normally would, and if you want to view the JavaScript & CSS source for your current page just tap the Action icon and choose JSView.
To enable the Safari extension, launch Safari, tap the action button on the toolbar, scroll right to the end, then tap More. Make sure JSView is enabled, then position it wherever you want it in the list of Safari actions, and tap Done.