Try it out:
If you aren't sure how to get started, check out some of my experiments.
For instance, did you know that using the Boolean() constructor is perhaps the slowest way to create a boolean? In some cases it can be as much as an order of magnitude slower than alternate methods.
Also, if you've been using a for..in loops when they aren't necessary, your code is probably running more than ten times slower than it has to if you'd used a typical for-loop and cached the length.
Oh, and the last bit for now is that you better not even think of omitting the "var" statement when creating a new variable. Doing so could be slowing you down by two orders of magnitude!
Look for some more specific, in depth studies to come. What examples can you come up with?