Question

If I attach an additional property to an object, does it have to go at the end, or can I put it at a specified position.

function reassign(obj){
  delete obj.c;
  obj.c = "new three";

  var t = "<table border=\"1\">";
  for (var i in obj){
    t += "<tr><td>" + obj[i] + "</td></tr>"; 
  }
  t += "</table>";
  return t;
}

var obj = {
  a : "one",
  b : "two",
  c : "three",
  d : "four" 
};

var reassigned = reassign(obj);
document.write(reassigned);

Would it be possible somehow to put the new obj.c in the third position again after it’s been deleted, rather than having it appended to the end? Of course I could skip the delete part. But even without that, I could also for example intend inject alphabeta: "one point five" into the second position. Is it possible? Thanks!

jsbin

Answer 1

Array elements are ordered; object properties are not. You should never assume that object properties will be iterated in a particular order.

If order is important to you, create a new order:[] property which contains an array of property names, and you can iterate through that:

var obj = {
  a : "one",
  b : "two",
  c : "three",
  d : "four",
  order : ['a','b','c','d']
};