var MAX_ADULTS     = 5; 
var MAX_INFANTS    = 5;
var MAX_CHILDREN   = 3;
var MAX_YOUTHS     = 5;
var MAX_PASSENGERS = 5;

function plus(forId)
{
var inputs = document.getElementById(forId);
var iAdult=document.getElementById("add-in-1");
var iYouth=document.getElementById("add-in-2");
var iChildren=document.getElementById("add-in-3");
var iInfant=document.getElementById("add-in-4");
  if (inputs.name == "numYouths") {
    iAdult.value=0;
    iChildren.value=0;
    iInfant.value=0;
    var numYouths = parseInt(iYouth.value);
    if (numYouths >= MAX_YOUTHS) {
      return;
    }
  } else {
      iYouth.value=0;
      var numAdults = parseInt(iAdult.value);
      var numChildren = parseInt(iChildren.value);
      var numInfants = parseInt(iInfant.value);
      var totalPassengers = numAdults + numChildren;
      if (inputs.name == "numAdults") {
        if (numAdults >= MAX_ADULTS || totalPassengers >= MAX_PASSENGERS) {
          return;
        }
      } else if (inputs.name == "numChildren") {
      
        if (numChildren >= MAX_CHILDREN || totalPassengers >= MAX_PASSENGERS) {
          return;
        }
        if (numAdults == 0) {
          iAdult.value=1;
        }
      } else if (inputs.name == "numInfants") {
        if (numAdults > numInfants) {
          iInfant.value++;
          return;
        }
        if (numInfants >= MAX_INFANTS || totalPassengers >= MAX_PASSENGERS) { 
          return;
        }
        if (numAdults <= numInfants) {
          iAdult.value++;
        }
    }
}
inputs.value++;
}

function minus(forId)
{
var inputs = document.getElementById(forId);
var iAdult=document.getElementById("add-in-1");
var iYouth=document.getElementById("add-in-2");
var iChildren=document.getElementById("add-in-3");
var iInfant=document.getElementById("add-in-4");

  var numAdults = parseInt(iAdult.value);
  if (inputs.name == "numAdults") {
    if (numAdults == 1) {
      return;
    }
  }
  
  var numYouths = parseInt(iYouth.value);
  if (inputs.name == "numYouths") {
    if (numYouths == 1) {
      return;
    }
  }
if (inputs.value > 0)
{
inputs.value--;
}
  
  var numInfants = parseInt(iInfant.value);
  if (inputs.name != "numChildren" && (numAdults <= numInfants && numInfants > 0)) {
    iInfant.value=numAdults - 1;
  }    
}