Mastering JavaScript Functional Programming - Second Edition

Partial application with closures

Let's examine yet another way of doing partial application, by using closures. (You may want to go over that topic in Chapter 1, Becoming Functional – Several Questions.) This way of doing partial application will behave in a fashion somewhat reminiscent of the curry() functions we wrote earlier in this chapter, and solve the lack of flexibility that we mentioned at the end of the previous section. Our new implementation would be as follows:

const partialByClosure = (fn, ...args) => {  const partialize = (...args1) => (...args2) => {    for (let i = 0; i < args1.length && args2.length; i++) {      if (args1[i] === undefined) {        args1[i] = args2.shift();      }    }    const allParams = [...args1, ...args2]; return (allParams.includes(undefined) ...