Find largest gap in a list of appointments

ArrayChallenge

function ArrayChallenge(strArr) { 

  // code goes here  
  let appointmentArray = [];
  let isStartPM = Boolean;
  let isEndPM = Boolean;
  let appointmentArrayMinutes = [];
  let largestGapMinutes = 0;  // Initialize to 0 so overlapping appointments will 0 minutes gap.
  let start;
  let end;
  let startMinutes;
  let endMinutes;
  let gapStartMinutes;
  let gapEndMinutes;
  let gapSizeMinutes;
  let largestGapHoursOnly;
  let largestGapMinutesRemainder;
  let largestGapHHMM;

  // Generate an appointment array using minutes past midnight
  for(let i = 0;i < strArr.length; i++) {
    appointmentArray[i] = strArr[i].split('-');
    
    // Build array in minutes past midnight
    isStartPM = false;
    isEndPM = false;
    start = appointmentArray[i][0];
    end = appointmentArray[i][1];
    startMinutes = parseInt(start.slice(0,2)) * 60 + parseInt(start.slice(3,5));
    endMinutes = parseInt(end.slice(0,2)) * 60 + parseInt(end.slice(3,5));
    if (start.slice(5,7) == "PM") {
      isStartPM = true;
    };
    if (end.slice(5,7) == "PM") {
      isEndPM = true;
    };

    // if PM add 12 hours
    if ((parseInt(start.slice(0,2)) < 12 ) && isStartPM) {
      startMinutes = startMinutes + 12 * 60;
    }
    if ((parseInt(end.slice(0,2)) < 12 ) && isEndPM) {
      endMinutes = endMinutes + 12 * 60;
    }

    // build the array
    appointmentArrayMinutes.push([startMinutes,endMinutes]);
  }

  // Sort the array
  appointmentArrayMinutes.sort();
  
  // Loop to find the largest gap in minutes
  for(let i = 0; i < (appointmentArrayMinutes.length -1) ; i++) {
    gapStartMinutes = appointmentArrayMinutes[i][1];
    gapEndMinutes = appointmentArrayMinutes[i + 1][0];
    gapSizeMinutes = gapEndMinutes - gapStartMinutes;
    if (gapSizeMinutes > largestGapMinutes) {
      largestGapMinutes = gapSizeMinutes;
    }
  }

  // Return the largest gap in HH:MM format
  largestGapHoursOnly = parseInt(largestGapMinutes / 60);
  largestGapMinutesRemainder = largestGapMinutes % 60;
  largestGapHHMM = largestGapHoursOnly.toString().padStart(2,'0') + ":" + largestGapMinutesRemainder.toString().padStart(2,'0');
  return largestGapHHMM; 
}



// keep this function call here 
console.log(ArrayChallenge(readline()));



// ["12:15PM-02:00PM","09:00AM-10:00AM","10:30AM-12:00PM"]