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

Yep, it is totally ok. You do not need to re-invent what does exist already, and your code will be more useable for another developer.

EDIT: You might want to use object instead a simple string because you would like to send some other information.

For example, you might want to send the content of another input which will be developed later.

You should not use stringify is the target browser is IE7 or lesser without adding json2.js.