/***********************************************************

  FUNCTIONS TO CALLBACK 

***********************************************************/

​

function add(a, b) { return a + b; }

​

function subtract(a, b) { return a - b; }

​

function multiply(a, b) { return a * b; }

​

function divide(a, b) { return a/b; }

​

function modulus(a, b) { return a % b; }

​

function randomInt() { 

  return Math.floor(Math.random() * 1000);

}

​

/***********************************************************

  VARIABLE ASSIGNMENTS 

***********************************************************/

​

var x = parseInt(prompt("What is X?")) || randomInt();

var y = parseInt(prompt("What is y?")) || randomInt();

​

​

/***********************************************************

  OUR AWESOME CALLBACK FUNCTION 

***********************************************************/

​

function calculate(a, b, callback) {

  return callback(a, b);

}

​

/***********************************************************

  LOGGING OUR CALLBACK FUNCTION RESULTS

***********************************************************/

​

console.log("For an x of " + x + " and a y of " + y + ":");

console.log("add      = " + calculate(x, y, add));

console.log("subtract = " + calculate(x, y, subtract));

console.log("multiply = " + calculate(x, y, multiply));

console.log("divide   = " + calculate(x, y, divide));

console.log("modulus  = " + calculate(x, y, modulus));