Mastering JavaScript Functional Programming

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 a given function would work only once:

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

This is a perfectly fine solution, 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. That's easy to fix, however; all we require is adding a return statement. However, that wouldn't be enough; what would the function return if called more times? We can take a page out of the memoizing solution ...