Mastering JavaScript Functional Programming

Partial application with closures

Let's examine yet another way of doing partial application, which will behave in a fashion somewhat reminiscent of the curry() functions we wrote earlier in this chapter, and solve the deficiency we mentioned at the end of the previous section:

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) ||        allParams.length < fn.length            ? partialize            : fn)(...allParams);    };        return partialize(...args);};

Wow, a longish bit of code! The key is the inner function partialize(). Given a list ...