Mastering JavaScript Functional Programming - Second Edition

Timing functions

Another possible application for wrapped functions is to record and log the timing of each function invocation in a fully transparent way. Simply put, we want to be able to tell how long a function call takes, most likely for performance studies. However, in the same way we dealt with logging, we don't want to have to modify the original function and will use a higher-order function instead. 

If you plan to optimize your code, remember the following three rules: Don't do it, Don't do it yet, and Don't do it without measuring. It has been mentioned that much bad code arises from early attempts at optimization, so don't start by trying to write optimal code, don't try to optimize until you recognize the need for it, and don't ...