a light toJSONString() implement

gistfile1.txt

Object.prototype.toJSONString = function () {
    var i, x, content, returnValue;
    if (this instanceof Array) {
        for (i = 0; i < this.length; i++) {
            if (this[i] !== undefined) {
                if (this[i] != null) {
                    content = content ? (content + "," + this[i].toJSONString()) : this[i].toJSONString();
                } else {
                    content = content ? (content + "," + "null") : "null";
                }
            } else {
                content = content ? (content + "," + "undefined") : "undefined";
            }
        }
        returnValue = "[" + content + "]";
    } else {
        for (x in this) {
            if (this.hasOwnProperty(x)) {
                if (this[x] !== undefined) {
                    if (this[x] != null) {
                        content = content ? (content + "," + x + ":" + this[x].toJSONString()) : (x + ":" + this[x].toJSONString());
                    } else {
                        content = content ? (content + "," + x + ":" + "null") : (x + ":" + "null");
                    }
                } else {
                    content = content ? (content + "," + x + ":" + "undefined") : (x + ":" + "undefined");
                }
            }
        }
        returnValue = "{" + content + "}";
    }
    return returnValue;
};
Boolean.prototype.toJSONString = function () {
    return this.toString();
};
Number.prototype.toJSONString = function () {
    return this.toString();
};
String.prototype.toJSONString = function () {
    var temp;
    temp = this.toString();
    temp = temp.replace(/(\\|\")/g, "\\$1");
    temp = temp.replace("\n", "\\n");
    temp = temp.replace("\r", "\\r");
    temp = temp.replace("\f", "\\f");
    temp = temp.replace("\r", "\\r");
    return "\"" + temp + "\"";
};
Function.prototype.toJSONString = function () {
    return this.toString();
};
RegExp.prototype.toJSONString = function () {
    return this.toString();
};
Math.toJSONString = function () {
    return "Math";
};
Date.prototype.toJSONString = function () {
    return "new Date(" + this.getTime() + ")";
};