In JS web apps, the most common speed constraint you'll encounter is how fast you can render views and update the DOM. Imagine trying to render 500 list items .

In JS web apps, the most common speed constraint you'll encounter is how fast you can render views and update the DOM. Imagine trying to render 500 list items ... say, contacts in an address book -- you don't really want that to take 3 seconds on an iPad. If it works for your needs, that's fantastic, but it's nice to be aware of the performance relative to alternatives that accomplish the same goal.