Is it just me, or for this example does the "dispatch table" seem way more complex (and likely less efficient) than the switch statement? The original is not difficult at all to interpret.
The performance is substantially different. The dispatch table is ~75% slower (in chrome). http://jsperf.com/switchvsdispatchtable
One thing I really like about dispatch tables is that it forces the developer to only be able to handle the decision logic. The number of times I've had to cleanup a switch with 20-30 lines under each condition (sometimes including another switch) is too many to count.
Of course those are, they're doing very different things in that test case. Your first case is just returning a value, and the second is executing a function to return a value. Here's a better comparison, http://jsperf.com/switchvsdispatchtable/2
There's nothing inherently slow about dispatch tables, it all about how you implement them. As someone else mentioned, the OP should be using bind to reduce the # of function calls instead of executing a function which executes a function.
And to top it of, you can dynamically add new commands to the dispatch table which you can't to a switch.
There is no fundamental difference between either approaches except the runtime cost. If you need conditonals, use them. If you need a lookup table, use them. Keep the code predictable.