These are two examples on how to chain promises that need to be executed one after the other.

promise-chaining.js

    const readSession = function(portHandle, sectors) {
        // this holds the result
        let result = [];
        // this is the entry point of the recursive func
        let _readAll = function(sectorsToRead) {
            // when there's no more sectore to read
            // we stop and return the result
            if (sectorsToRead.length === 0) {
                return result;
            }

            // read the data from serial on the current sector
            return Device.readChunk(portHandle, sectorsToRead.shift()).then((dataFromSerial) => {
                // once we get the data, save it
                result.push(dataFromSerial);
                // call to read the next sector
                return _readAll(sectorsToRead);
            });
        }
        // main call to the start recursive function
        return _readAll(sectors);
    }

    const readSession1 = function(portHandle, sectors) {
        // setup the buffer that will contain all the sector data
        let fullBuffer = new Buffer(PAYLOAD_LEN * sectors.length);

        // this will iterate through the sector array starting from the first element
        return sectors.reduce(function(previous, currentSector, index) {
            // previous is a promise
            // initial value is a promise with an empty buffer
            return previous.then(function(previousValue) {
                // we read the sector data here from serial
                return Device.readChunk(portHandle, currentSector).then((dataFromSerial) => {
                    // copy the data to the buffer that will contain all the data
                    dataFromSerial.copy(previousValue, PAYLOAD_LEN*index);
                    // important! return the modified buffer, will be used in the next iteration
                    return previousValue;
                });
            })
        // we shall start with an empty buffer
        }, Promise.resolve(fullBuffer));
    }