'use strict';

// Sync function to async

const last = (arr) => arr[arr.length - 1];

const asyncify = (fn) => (...args) => {

const callback = last(args);

args.pop();

process.nextTick(() => {

callback(null, fn(...args));

});

};

// Functions

const f1 = (par) => par;

const f2 = (par) => par;

const f3 = (par) => par;

const f4 = (par) => par;

// Usage

const af1 = asyncify(f1);

const af2 = asyncify(f2);

const af3 = asyncify(f3);

const af4 = asyncify(f4);

af1('value2', (e, data) => {

af2(data, (e, data) => {

af3(data, (e, data) => {

af4(data, (e, data) => {

console.dir({ data });

});

});

});

});

console.log(f4(f3(f2(f1('value')))));