_.isFunction(a) vs. typeof a === 'function'? javascript

Question

I think it might be only performance case - http://jsperf.com/comparing-underscore-js-isfunction-with-typeof-function/2

And seems that typeof is faster.

Answer 1

There is no reason not to use typeof.

Not only is it faster but the ECMAScript specification ensures that all functions have a type of "function" and that only functions can have a type of "function" :

This operator was specifically designed to get the type of a value, so why not use it ?