callback-hell.js

// Define some functions and pretend they need to 
// be asynchronous just for demonstration purposes

function plus(n1, n2, cb) {
  return cb(n1+n2);
}

function minus(n1, n2, cb) {
  return cb(n1-n2);
}

function mul(n1, n2, cb) {
  return cb(n1*n2);
}

// Let's go to callback hell
plus(42, 17, function(res1) {
  minus(res1, 12, function(res2) {
    mul(res2, 10, function(res3) {

      // Will print out 470
      console.log(res3);

    })
  });
});