/* Disable API call because we don't have that API, 

  replace similar callback function for demo purpose

*/

​

let resultA, resultB, resultC;

​

function addAsync (num1, num2, callback) {

    // use the famous jQuery getJSON callback API

//  return $.getJSON('http://www.example.com', {

//      num1: num1,

//      num2: num2

//  }, callback);

    const cb = $.Callbacks();

    cb.add(callback);

    cb.fire(num1+num2);

}

​

addAsync(1, 2, success => {

    // callback 1

    resultA = success; // you get result = 3 here

    addAsync(resultA, 3, success => {

        // callback 2

        resultB = success; // you get result = 6 here

​

        addAsync(resultB, 4, success => {

            // callback 3

            resultC = success; // you get result = 10 here

            console.log('total' + resultC);

            console.log(resultA, resultB, resultC);

        });

    });

});