How to update geojson markers periodically - leaflet

Question

What I am trying to do is to use Leaflet with OSM map,
and load data from PHP in GeoJSON format + update periodically.
I can manage to display a map, load data, but do not know how to update points instead of still adding a new ones.
function update_position() {
$.getJSON('link_to_php', function(data) {
//get data into object
var geojsonFeature = JSON.parse(data);
// how to remove here old markers???
//add new layer
var myLayer = L.geoJSON().addTo(mymap);
//add markers to layet
myLayer.addData(geojsonFeature);
setTimeout(update_position, 1000);
});
}
update_position();
have tried mymap.removeLayer("myLayer"); but this seems to now work inside of function. Please help

Answer 1

L.geoJSON extends from LayerGroup which provide a function named clearLayers(docs), so you call that to clear markers from the layer.
Also, it is recommended that you put the layer variable outside the function:
var geoJSONLayer = L.geoJSON().addTo(mymap);
function update_position() {
$.getJSON('link_to_php', function(data) {
//get data into object
var geojsonFeature = JSON.parse(data);
geoJSONLayer.clearLayers();
//add markers to layet
geoJSONLayer.addData(geojsonFeature);
setTimeout(update_position, 1000);
});
}
update_position();