Question

I have functions that when a li element is clicked markers are added to the map. If another li is clicked then the original markers are removed and the new one appearr.

The issue I am having is that the markers are placed on the map when a li is clicked for the first time. When a second li is clicked the markers are removed but the new ones are not added. I get no error in firebug. I cant see what I am missing.

$(document).ready(function() {

    $(".markerSelection").click(function() {
      var selectionId = $(this).attr("id");
      drop(selectionId);
    }); 
});



var markers = {
    shopping : [
    new google.maps.LatLng(52.26183, -7.11339),
    new google.maps.LatLng(52.26134, -7.11226),
    new google.maps.LatLng(52.26067, -7.11181),
    new google.maps.LatLng(52.26003, -7.11033)],
    cars : [
    new google.maps.LatLng(52.26183, -7.11339),
    new google.maps.LatLng(52.26134, -7.11226),
    new google.maps.LatLng(52.26067, -7.11181),
    new google.maps.LatLng(52.26003, -7.11033)] 
};

var iterator = 0; 

function drop(selectionId) {
    clearOverlays();
    for (var i = 0; i < markers[selectionId].length; i++) {
    setTimeout(function() {
    addMarker(selectionId);
    }, i * 200);
    }
}

function addMarker(selectionId) {
    marker = new google.maps.Marker({
    position: markers[selectionId][iterator],
    map: map,
    draggable: false,
    animation: google.maps.Animation.DROP
    });
    iterator++;
    markersArray.push(marker);
}

// Removes the overlays from the map, but keeps them in the array
function clearOverlays() {
  if (markersArray) {
    for (i in markersArray) {
      markersArray[i].setMap(null);
    }
  }
}

Answer 1

I reviewed your code one more time, and I think the problem is with iterator, which is initialized to 0 in global scope. That is why the first time it works okay, but after that, indices exceed. It seems you should set it to zero at the beginning of the drop() function.
However it makes more sense if you pass index as a second parameter of addMarker() instead of an outer variable which is handled in drop() and complicate you code.