The syntax highlighting is tough but check out this fiddle for pretty printing a json object entered in a text area. Do note that the JSON has to be valid for this to work. (Use the dev console to catch errors.) Check jsLint for valid json.

The HTML:

Copy<textarea id="myTextArea" cols=50 rows=10></textarea>
<button onclick="prettyPrint()">Pretty Print</button>

The js:

Copyfunction prettyPrint() {
    var ugly = document.getElementById('myTextArea').value;
    var obj = JSON.parse(ugly);
    var pretty = JSON.stringify(obj, undefined, 4);
    document.getElementById('myTextArea').value = pretty;
}

First try simple input like: {"a":"hello","b":123}

Simple pretty printing of JSON can be done rather easily. Try this js code: (jsFiddle here)

Copy// arbitrary js object:
var myJsObj = {a:'foo', 'b':'bar', c:[false,2,null, 'null']};

// using JSON.stringify pretty print capability:
var str = JSON.stringify(myJsObj, undefined, 4);

// display pretty printed object in text area:
document.getElementById('myTextArea').innerHTML = str;

For this HTML:

Copy<textarea id="myTextArea" cols=50 rows=25></textarea>

And check out JSON.stringify documentation.

this should be pretty simple... take a look if this jsFiddle fit your needs

   var yourObject = {"address":{"House_Number":505,
    "Street_Direction":"",
    "Street_Name":"Claremont",
    "Street_Type":"Street",
    "Apt":"15L",
    "Burough":"Brooklyn",
    "State":"NY",
    "Zip":"10451",
    "Phone":"718-777-7777"},
    "casehead":0,
    "adults":[{"Last_Name":"Foo",
    "First_Name":"A",
    "Sex":"M",
    "Date_Of_Birth":"01011980"}],
    "children":[]};

var textedJson = JSON.stringify(yourObject,undefined, 2);
document.getElementById("json-area").value = textedJson

;

P.S. i've used jQuery just to speed-up the example but the function on which you should focus is JSON.stringify