index.js

var objToString = Object.prototype.toString;
var objKeys = Object.keys || function(obj) {
		var keys = [];
		for (var name in obj) {
			keys.push(name);
		}
		return keys;
	};

function stringify(val, isArrayProp) {
	var i, max, str, keys, key, propVal, toStr;
	if (val === true) {
		return "true";
	}
	if (val === false) {
		return "false";
	}
	switch (typeof val) {
		case "object":
			if (val === null) {
				return null;
			} else if (val.toJSON && typeof val.toJSON === "function") {
				return stringify(val.toJSON(), isArrayProp);
			} else {
				toStr = objToString.call(val);
				if (toStr === "[object Array]") {
					str = '[';
					max = val.length - 1;
					for(i = 0; i < max; i++) {
						str += stringify(val[i], true) + ',';
					}
					if (max > -1) {
						str += stringify(val[i], true);
					}
					return str + ']';
				} else if (toStr === "[object Object]") {
					// only object is left
					keys = objKeys(val).sort();
					max = keys.length;
					str = "";
					i = 0;
					while (i < max) {
						key = keys[i];
						propVal = stringify(val[key], false);
						if (propVal !== undefined) {
							if (str) {
								str += ',';
							}
							str += JSON.stringify(key) + ':' + propVal;
						}
						i++;
					}
					return '{' + str + '}';
				} else {
					return JSON.stringify(val);
				}
			}
		case "function":
		case "undefined":
			return isArrayProp ? null : undefined;
		case "string":
			return JSON.stringify(val);
		default:
			return isFinite(val) ? val : null;
	}
}

module.exports = function(val) {
	var returnVal = stringify(val, false);
	if (returnVal !== undefined) {
		return ''+ returnVal;
	}
};