<form>
    <input type="text" id="lat" name="lat">
    <input type="text" id="lon" name="lon">
</form>

<script>
    function show_position(position) {
        document.getElementById('lat').value = position.coords.latitude;
        document.getElementById('lon').value = position.coords.longitude;
    }

    function get_geolocation(){
        if (navigator.geolocation) {
            navigator.geolocation.getCurrentPosition(show_position);
        }
    }

    document.addEventListener("DOMContentLoaded", function(event) {
        get_geolocation();
    });
</script>