Object.toString（）-> [对象对象]

The following code send by using Ajax a json :

var geojson = new Object();
geojson["type"] = "FeatureCollection";
geojson["zone_type"] = "Zone";
$.ajax({
  url : url,
  type : 'POST',
  data : geojson,
  dataType : 'json',
});

However, when I ask in the console "geojson" and when I look the request in the network :

geojson = "[object Object]"

Actually, I should have the object :

geojson = {type:FeatureCollection,zone_type:Zone}

Shouldn't I ?

var geojson = new Object();
geojson["type"] = "FeatureCollection";
geojson["zone_type"] = "Zone";
$.ajax({
  url : url,
  type : 'POST',
  data : JSON.stringify(geojson),
  dataType : 'json',
});

If I add JSON.stringify(geojson) indeed, I get correctly :

geojson = {"type":"FeatureCollection","zone_type":"warning_zone"}

Thank you very much @SLYcee