function sample() {
  var result = sforce.connection.describeSObject("CustomObject__c");

  alert("---------- fields ---------");
  for (var i=0; i<result.fields.length; i++) {
    var fld = result.fields[i];
    alert(fld);
  }

  alert("---------- childRelationships ---------");
  for (var i=0; i<result.childRelationships.length; i++) {
    var cr = result.childRelationships[i];
    alert(cr);
  }

  alert("---------- recordTypeInfos ----------");
  for (var i=0; i<result.recordTypeInfos.length; i++) {
    var rt = result.recordTypeInfos[i];
    alert(rt);
  }
}