council_meeting_preparation.js

function ServantA() {
  //for simplicity hidden the implementation
  function cleaningHall() {
    return new Promise(cleaningHallPromiseHandler);
  }

  return {
    cleaningHall: cleaningHall
  };
}

function servantB() {
  //for simplicity hidden the implementation
  function arrangeTables() {
    return new Promise(arrangeTablesPromiseHandler);
  }

  return {
    arrangeTables: arrangeTables
  };
}

function servantC() {
  //for simplicity hidden the implementation
  function prepareLunch() {
    return new Promise(prepareLunchPromiseHandler);
  }

  return {
    prepareLunch: prepareLunch
  };
}

//Three task at time
function King() {
  let servantA = ServantA();
  let servantB = ServantB();
  let servantC = ServantC();

  //King has to keep track up servants work status since each servants works in parallel
  let isHallCleaned = false;
  let isTablesArranged = false;
  let isLunchReady = false;

  function canBeginCouncil() {
    if(isHallCleaned === true &&
      isTablesArranged === true &&
      isLunchReady === true) {
        //Begin the council
      }
  }

  servantA.cleaningHall()
    .then(function promiseFulfilled() {
      isHallCleaned = true;
      //Since servants are working independently there is no order in finishing work so
      //King has to check overall progress when ever each servant completes his/her work
      canBeginCouncil();
    })
    .catch(function promiseFailed(reason) {
      isHallCleaned = false;
    });

  servantB.arrangeTables()
    .then(function promiseFulfilled() {
      isTablesArranged = true;
      canBeginCouncil();
    })
    .catch(function promiseFailed(reason) {
      isTablesArranged = false;
    });

  servantC.prepareLunch()
    .then(function promiseFulfilled() {
      isLunchReady = true;
      canBeginCouncil();
    })
    .catch(function promiseFailed(reason) {
      isLunchReady = false;
    });
}

//Wake up the King
King();