Web applications are getting more and more complex from year to year. Couple of years ago nobody cared about the memory leaks on the web pages (yeah, they were really a set of web pages, but not web applications). Even if you forget to clean up some memory – it’s not expected, that user will spend a lot of time on the same page. There were a lot of navigation links, which removed information about the entire page from memory and loaded new page.
But now you cannot relate on this behavior, because now web sites turned into web applications. User loads one small HTML file, one script file and some other stuff (like CSS and images) and that’s it. Making requests from browser to servers user can stay on on the “page” for ages. In the worst scenario you will receive a report from production user: “Oh, your application is crashing after 60 hours of using”.
It looks like you have leaking memory in the application.