new Chainable(4).timesTwo().plusTwo().timesTwo()

gistfile1.txt

var assert = require('assert');
 
var isNumber = function (number) {
    return typeof number === 'number';
};
 
var timesTwo = function (number, callback) {
    process.nextTick(function () {
        if (isNumber(number)) {
            callback(null, number * 2);
        }
        else {
            callback(new Error('You did not pass a number'));
        }
    });
};
 
var plusTwo = function (number, callback) {
    process.nextTick(function () {
        if (isNumber(number)) {
            callback(null, number + 2);
        }
        else {
            callback(new Error('You did not pass a number'));
        }
    });
};
 
var timesTwoPlusTwo = function (number, callback) {
    timesTwo(number, function (err, result) {
        if (err) {
            callback(err);
        }
        plusTwo(result, callback);
    });
};

class Chainable{
  constructor(i){
    this.val = i;
  }
  
  timesTwo () {
    this.val *= 2;
    return this
  }

  plusTwo () {
    this.val += 2;
    return this
  }
}

console.log(new Chainable(4).timesTwo().plusTwo().timesTwo());
 
// 1. new Chainable(4).timesTwo().plusTwo().timesTwo() = 20

// 2. const chainedFunctions = chain(timesTwo, plusTwo, plusTwo, timesTwo);
//    chainedFunctions(4) = 48

timesTwoPlusTwo(4, function (err, result) {
    assert.equal(result, 10);
});