Can i save the features on selecting points into same json file?

draw.on('drawend',
      function(evt) {
        console.log(evt.feature);
        var parser = new ol.format.GeoJSON();
        var features = floodAlertLayer.getSource().getFeatures();
        var featuresGeoJSON = parser.writeFeatures(features);
        var text = JSON.stringify(featuresGeoJSON);
     //   document.getElementById('info').innerHTML = text;
       // alert(features.get("COUNTY"));
        $.ajax({
            url: 'FloodAlert.json',
            type: 'POST',

            data: text


        }).then(function(response) {
            console.log(response);
        });
      },
    this);
  }`