let resultA, resultB, resultC;

​

function addAsync(num1, num2) {

    // use ES6 fetch API, which return a promise

//  return fetch(`http://www.example.com?num1=${num1}&num2=${num2}`)

//      .then(x => x.json());

    return Promise.resolve(num1 + num2);

}

​

addAsync(1, 2)

    .then(success => {

        resultA = success;

        return resultA;

    })

    .then(success => addAsync(success, 3))

    .then(success => {

        resultB = success;

        return resultB;

    })

    .then(success => addAsync(success, 4))

    .then(success => {

        resultC = success;

        return resultC;

    })

    .then(success => {

        console.log('total: ' + success)

        console.log(resultA, resultB, resultC)

    });