Global map variable in Leaflet

Question

I'm working in Leaflet, trying to do some zoom methods to remove layers when I zoom out.

var map;

//function to instantiate the Leaflet map
function createMap(){
//create the map
map = L.map('map', {
    //set geographic center
    center: [41.4, -110],
    //set initial zoom level
    zoom: 4,
    maxZoom: 8,
    minZoom: 2
});


//add OSM base tilelayer
L.tileLayer('http://{s}.basemaps.cartocdn.com/dark_all/{z}/{x}/{y}.png', {
    //set attribute info (source)
    attribution: '&copy; <a href="http://www.openstreetmap.org    /copyright">OpenStreetMap contributors</a>'
    //and add it to map

}).addTo(map);
 L.geoJson(worldCountries).addTo(map);

};

However, I am now trying to add some listener event that will remove layers when the map is zoomed.

map.on('zoomend', function () {
if (map.getZoom() > 4) {
    map.removeLayer(worldCountries);
}

});

$(document).ready(createMap);

I get an error saying "map is undefined." I thought I declared it globally at the very beginning of the script? Indeed, I can't seem to access the map variable outside of the createMap function so this seems to be the problem.