var obj = {
  x: 45,
  b: {
    func: function(){alert('a')},
    name: "b"
  },
  a: "prueba"
};

var nw = moveProp(obj, "a", "x"); //-- move 'a' to position of 'x'
console.log(nw, obj);


//--

function moveProp(obj, moveKey, toKey){
  var temp = Object.assign({}, obj)
  var tobj;
  var resp = {};

  tobj = temp[moveKey];
  delete temp[moveKey];
  for(var prop in temp){
    if (prop===toKey) resp[moveKey] = tobj;
    resp[prop] = temp[prop]; 
  }
  return resp;
}