var map = L.map('map').setView([20.5, -0.09], 3);
L.tileLayer('http://{s}.tile.osm.org/{z}/{x}/{y}.png').addTo(map);
var southWest = L.latLng(-60.5, -90),
northEast = L.latLng(60.5, 90);
var bounds = L.latLngBounds(southWest, northEast);
map.setMaxBounds(bounds);
map.on('drag', function() {
map.panInsideBounds(bounds, { animate: false });
});