Mastering JavaScript Functional Programming - Second Edition

Doing things once, revisited

Back in Chapter 2, Thinking Functionally – A First Example, we went through an example of developing an FP-style solution for a simple problem: fixing things so that a given function works only once. The following code is what we wrote back then:

const once = func => {  let done = false;  return (...args) => {    if (!done) {      done = true;      func(...args);    }  };};

This is a perfectly fine solution; it works well and we have nothing to object to. We can, however, think of a variation. We could observe that the given function gets called once, but its return value gets lost. This is easy to fix: all we need to do is add a return statement. However, that wouldn't be enough; what would the function return if it's called more? ...