var map = L.map('map').setView([51.505, -0.09], 13).setZoom(2);

L.tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png?{foo}', {
    foo: 'bar',
    attribution: 'Map data &copy; <a href="https://www.openstreetmap.org/">OpenStreetMap</a> contributors, <a href="https://creativecommons.org/licenses/by-sa/2.0/">CC-BY-SA</a>'
}).addTo(map);

var marker = L.marker([0, 0], draggable = true).addTo(map);

var LatLng = marker.getLatLng();

let coordinates_input = document.getElementById('latlng');

function onMapClick(e) {
    marker.setLatLng(e.latlng);
    LatLng = marker.getLatLng();
    // console.log(LatLng);
    lat = LatLng['lat'];
    lng = LatLng['lng'];
    coordinates_input.value = lat + ', ' + lng;
}

map.on('click', onMapClick);