Script to show the behavior of callbacks and promises

Script.js

(()=>{
  console.log("start");
  secondFunction().then(function(secondNumber){
    console.log("result first promise "+secondNumber);
  });
  myFunction((newNumber)=>{
    var lNumber = 20 + newNumber;
    console.log(lNumber);
  });
  console.log("end");

})()

function myFunction(callback){
  console.log("callback");
  var mNumber = 2+3;

  return callback(mNumber);
}


function secondFunction(){
  return new Promise(function(resolve, reject){
    console.log("promise");
    thirdFunction().then(function(thirdNumber){
      console.log("result second promise "+thirdNumber);
    })
    console.log("end first promise");
    return resolve(2+15);
  });
}

function thirdFunction(){
  return new Promise(function(resolve, reject){
    console.log("second promise");
    return resolve(1234);
  })
}