function properties(){ 
  var myObj = { "name": "John", "age": 30, "car": null };
  for (x in myObj) {
    document.getElementById("demo").innerHTML += "property:" + x + " value:" +  myObj[x] + "
";
// properties: x    values: myObj[x] 
  }
}

How to loop through all properties in a JSON object.