Part of map.js that adds and filters markers on the map.

map.js

    // Removes all markers on the map. 
    function clearOverlays(category) {
        if (markersArray) {
            for (i in markersArray) {
                if (category === undefined) {
                    markersArray[i].setMap(null);
                }
                else {
                    if (markersArray[i].val.Category.Name == category) {
                        markersArray[i].setMap(null);
                    }
                }
            }
        }
        markersArray.length = 0;
    }

    // Add all markers to the map.
    function allMap() {
        categoryArray.length = 0;
        $.getJSON("/Books/Map", function (data) {
            clearOverlays();
            $.each(data, function (key, val) {
                createMarker(map, new google.maps.LatLng(val.Latitude, val.Longitude), val.Title + "  \n" + val.Place, val);
            });
        });
    }
    allMap(); // This adds all markers when map.js is first interpreted onload.

    // Change the icons based on the zoomlevel
    google.maps.event.addListener(map, 'zoom_changed', function () {
        if (markersArray) {
            for (i in markersArray) {
                setInfoboxPixelOffset();
                markersArray[i].setIcon(RATLL.get_icon(markersArray[i].val, map.getZoom()));
            }
        }
        document.body.style.cursor = "default";
    });

    // Filter markers and only add them if their category is in the categoryArray.
    function filterMap() {
        $.getJSON("/Books/Map", function (data) {
            clearOverlays();
            $.each(data, function (key, val) {
                if ($.inArray(val.Category.Name, categoryArray) !== -1) {
                    createMarker(map, new google.maps.LatLng(val.Latitude, val.Longitude), val.Title + "\n" + val.Place, val);
                }
            });
        });
    }

    // Assign the map object to an element in the dom. Then it'll be accessible later on, outside of this closure.
    document.getElementById("map").map = map;
    
    // Click event and filtering for the fiction category / checkbox.
    $("#chk_fiction:checkbox").click(function () {
        var checked = $("#chk_fiction:checked");
        //console.log($("input[id=chk_all]").is(":checked"));
        if ($("input[id=chk_all]").is(":checked")) {
            $("input[id=chk_all]").attr("checked", false);
            clearOverlays();
        }
        if (checked.length > 0) {
            if ($.inArray("Fiction", categoryArray) === -1) {
                categoryArray.push("Fiction");
            }
            filterMap();
        } else {
            var index = $.inArray("Fiction", categoryArray);
            if (index > -1) {
                categoryArray.splice(index, 1);
            }
            filterMap();
        }
    });

    // Click event and filtering for the nonfiction category / checkbox.
    $("#chk_nonfiction:checkbox").click(function () {
        var checked = $("#chk_nonfiction:checked");
        if ($("input[id=chk_all]").is(":checked")) {
            $("input[id=chk_all]").attr("checked", false);
            clearOverlays();
        }
        if (checked.length > 0) {
            if ($.inArray("Nonfiction", categoryArray) === -1) {
                categoryArray.push("Nonfiction");
            }
            filterMap();
        } else {
            var index = $.inArray("Nonfiction", categoryArray);
            if (index > -1) {
                categoryArray.splice(index, 1);
            }
            filterMap();
        }
    });

    // Click event and filtering for the teen category / checkbox.
    $("#chk_teen:checkbox").click(function () {
        var checked = $("#chk_teen:checked");
        if ($("input[id=chk_all]").is(":checked")) {
            $("input[id=chk_all]").attr("checked", false);
            clearOverlays();
        }
        if (checked.length > 0) {
            if ($.inArray("Teen", categoryArray) === -1) {
                categoryArray.push("Teen");
            }
            filterMap();
        } else {
            var index = $.inArray("Teen", categoryArray);
            if (index > -1) {
                categoryArray.splice(index, 1);
            }
            filterMap();
        }
    });

    // Click event and filtering for the children category / checkbox.
    $("#chk_children:checkbox").click(function () {
        var checked = $("#chk_children:checked");
        if ($("input[id=chk_all]").is(":checked")) {
            $("input[id=chk_all]").attr("checked", false);
            clearOverlays();
        }
        if (checked.length > 0) {
            if ($.inArray("Children", categoryArray) === -1) {
                categoryArray.push("Children");
            }
            filterMap();
        } else {
            var index = $.inArray("Children", categoryArray);
            if (index > -1) {
                categoryArray.splice(index, 1);
            }
            filterMap();
        }
    });

    // Click event and filtering for the View All category / checkbox.
    $("#chk_all:checkbox").click(function () {
        var checked = $("#chk_all:checked");
        if (checked.length > 0) {
            clearOverlays();
            categoryArray.length = 0;
            $("input[id=chk_fiction]").attr("checked", false);
            $("input[id=chk_nonfiction]").attr("checked", false);
            $("input[id=chk_teen]").attr("checked", false);
            $("input[id=chk_children]").attr("checked", false);
            allMap();
        } else {
            categoryArray.length = 0;
            clearOverlays();
        }
    });