It really depends on what you are trying to do, creating an object in Javascript is pretty fast. Running a long calculation in Javascript will cause the browser to block as there is only one thread of execution. Though with modern browsers you can use web workers. But the two tend to be used for very different things.
I have to say Javascript is one of my favorite languages, and I spend about 80% of my work day working in it. (Though I will admit haskell and erlang are growing on me)