Javascript Deep Copy with Depth

deep-copy.js

/**
 * Deep Copy
 *
 * Creates a new object, copying the variables one by one into it.
 * Available as a GitHub Gist: https://gist.github.com/four43/f93647e8feaa54713cfe
 * @param {Object|Array} input The input object or array to copy.
 * @param {Number} [maxDepth] The max depth the function should recurse before passing by reference, default: 5
 * @param {Number} [depth] Starts at 0, used by recursion
 * @returns {Object|Array}
 * @private
 */
Object.prototype._deepCopy = function (input, maxDepth, depth) {
	if (maxDepth === undefined) {
		maxDepth = 5;
	}
	if (depth === undefined) {
		depth = 0;
	}

	if(depth > maxDepth) {
		return null;
	}

	// Handle the 3 simple types, and null or undefined
	if (input === null || input === undefined || typeof input !== "object") {
		return input;
	}

	// Date
	if (input instanceof Date) {
		var dateCopy = new Date();
		dateCopy.setTime(input.getTime());
		return dateCopy;
	}

	// Array
	if (input instanceof Array) {
		var arrayCopy = [];
		for (var i = 0, len = input.length; i < len; i++) {
			arrayCopy[i] = this._deepCopy(input[i], maxDepth, depth + 1);
		}
		return arrayCopy;
	}
	// Object
	if (input instanceof Object) {
		var newObj = {};
		for (var prop in input) {
			if (input.hasOwnProperty(prop)) newObj[prop] = this._deepCopy(input[prop]);
		}
		return newObj;
	}
}

Adding some limits (improvements?) to: http://stackoverflow.com/a/728694/387851

Added comment section.