There was a time when using too much javascript was considered bad programming practice.

Using Javascript for form validation, for example, could turn it into a disaster as it would be very easy for the user to turn off javascript on his browser, enter junk data (like 911 for email) and crash bang boom, there goes your backend. Of course middle-end(PHP) was the better answer (and it still is). In those days the much admired javascript was losing its essence. No one found it fun to add unnecessary browser shakes to their site and annoy users. Its purpose would have shrunk to sending occasional alerts, keeping time etc. But with AJAX gaining popularity, Javascript is reviving. AJAX is after all a form of Javascript. Online games, chatting, IM. It has managed to replace Flash in many areas (like IM, some simple games). Not only does AJAX save bandwidth for both the service provider and end user, it also saves the ever-valuable resource called ‘time’.