How to preserve order of elements in JSON with arrays

gistfile1.txt

/* what it might have looked like in XML */
<types>
  <foo>
    <category name="A">
      <item name="A1" />
      <item name="A2" />
    </catgory>
    <category name="B">
      <item name="B1" />
      <item name="B2" />
    </catgory>
    <category name="C">
      <item name="C1" />
      <item name="C2" />
    </catgory>
    <category name="D">
      <item name="D1" />
      <item name="D2" />
    </catgory>
  </foo>
  <bar>
    <category name="X">
      <item name="X1" />
      <item name="X2" />
    </catgory>
    <category name="Y">
      <item name="Y1" />
      <item name="Y2" />
    </catgory>
  </bar>
</types>

/* What you might be tempted to do */
{
	"foo": {
		"A": {
			"A1": {},
			"A2": {},
		},
		"B": {
			"B1": {},
			"B2": {},
		},
		"C": {
			"C1": {},
			"C2": {},
		},
		"D": {
			"D1": {},
			"D2": {},
		},
	},
	"bar": {
		"X": {
			"X1": {},
			"X2": {},
		},
		"Y": {
			"Y1": {},
			"Y2": {},
		}
	}
}

/* what you really need */
{
  "types": [
    {
      "name": "foo",
      "categories": [
        {
          "name": "A",
          "items": [
            {"name": "A1", "value": {}},
            {"name": "A2", "value": {}},
          ]
        },
        {
          "name": "B",
          "items": [
            {"name": "B1", "value": {}},
            {"name": "B2", "value": {}},
          ]
        },
        {
          "name": "C",
          "items": [
            {"name": "C1", "value": {}},
            {"name": "C2", "value": {}},
          ]
        },
        {
          "name": "D",
          "items": [
            {"name": "D1", "value": {}},
            {"name": "D2", "value": {}},
          ]
        }
      ]
    },
    {
      "name": "bar",
      "categories": [
        {
          "name": "X",
          "items": [
            {"name": "X1", "value": {}},
            {"name": "X2", "value": {}},
          ]
        },
        {
          "name": "Y",
          "items": [
            {"name": "Y1", "value": {}},
            {"name": "Y2", "value": {}},
          ]
        }
      ]
    },
  ]
}