AS3 JSON encoding

/** Contrary to many actionscript json libraries,
 * this function encodes properties of dynamic classes. */
public static function jsonEncode(obj:*, pretty:Boolean = false, maxLength:int = 60, depth:int = 0):String {
    const TAB_UNIT:String = "    ";

    var str:String;
    var key:String;
    var el:*;
    var arr:Array;
    var keyArr:Array;

    var tabStr:String;
    if (pretty) {
        tabStr = "";
        for (var i:int = 0; i < depth; i++)
            tabStr += TAB_UNIT;
    }

    if (obj is Number || obj is int || obj is Boolean)
    {
        return String(obj);
    }
    else if (obj is String)
    {
        //Escape backslashes
        str = replaceAll(obj as String, "\\", "\\\\");
        //Escape double quotes
        str = replaceAll(str, "\"", "\\\"");
        return '"' + str + '"';
    }
    else if (obj is Array)
    {
        arr = [];
        for each (el in obj)
            arr.push(jsonEncode(el, pretty, maxLength, depth + 1));

        if (pretty) {
            str = '[' + arr.join(', ') + ']';
            if (str.length > maxLength) {
                str = '[\n' +
                    tabStr + TAB_UNIT + arr.join(',\n' + tabStr + TAB_UNIT) + '\n' +
                    tabStr + ']';
            }
            return str;
        } else {
            return '[' + arr.join(',') + ']';
        }
    }
    else
    {
        keyArr = getObjKeys(obj);
        arr = [];
        for each (key in keyArr)
            arr.push('"' + key + (pretty ? '": ' : '":') + jsonEncode(obj[key], pretty, maxLength, depth + 1));

        if (pretty) {
            str = '{' + arr.join(', ') + '}';
            if (str.length > maxLength) {
                str = '{\n' +
                    tabStr + TAB_UNIT + arr.join(',\n' + tabStr + TAB_UNIT) + '\n' +
                    tabStr + '}';
            }
            return str;
        } else {
            return '{' + arr.join(',') + '}';
        }
    }
}

public static function replaceAll(target:String, p:String, repl:String):String {
    var str:String = target;
    var i:int = 0;
    var k:int;
    while ((k = str.indexOf(p, i)) >= 0) {
        str = str.substring(0, k) + repl + str.substring(k + p.length);
        i = k + repl.length;
    }
    return str;
}

/** Returns an array of public parameter names of a given instance
 * of some class and also dynamically set key names.*/
public static function getObjKeys(obj:Object):Array
{
    var arr:Array = [];
    for each (var qname:QName in ObjectUtil.getClassInfo(obj).properties)
        arr.push(qname.localName);

    return arr;
}