var hasOwn = Object.prototype.hasOwnProperty;
var toString = Object.prototype.toString;
var undefined;

var isPlainObject = function isPlainObject(obj) {
	'use strict';
	if (!obj || toString.call(obj) !== '[object Object]' || obj.nodeType || obj.setInterval) {
		return false;
	}

	var has_own_constructor = hasOwn.call(obj, 'constructor');
	var has_is_property_of_method = obj.constructor && obj.constructor.prototype && hasOwn.call(obj.constructor.prototype, 'isPrototypeOf');
	// Not own constructor property must be Object
	if (obj.constructor && !has_own_constructor && !has_is_property_of_method) {
		return false;
	}

	// Own properties are enumerated firstly, so to speed up,
	// if last one is own, then all properties are own.
	var key;
	for (key in obj) {}

	return key === undefined || hasOwn.call(obj, key);
};

module.exports = function extend() {
	'use strict';
	var options, name, src, copy, copyIsArray, clone,
		target = arguments[0],
		i = 1,
		length = arguments.length,
		deep = false;

	// Handle a deep copy situation
	if (typeof target === 'boolean') {
		deep = target;
		target = arguments[1] || {};
		// skip the boolean and the target
		i = 2;
	} else if (typeof target !== 'object' && typeof target !== 'function' || target == undefined) {
			target = {};
	}

	for (; i < length; ++i) {
		// Only deal with non-null/undefined values
		if ((options = arguments[i]) != null) {
			// Extend the base object
			for (name in options) {
				src = target[name];
				copy = options[name];

				// Prevent never-ending loop
				if (target === copy) {
					continue;
				}

				// Recurse if we're merging plain objects or arrays
				if (deep && copy && (isPlainObject(copy) || (copyIsArray = Array.isArray(copy)))) {
					if (copyIsArray) {
						copyIsArray = false;
						clone = src && Array.isArray(src) ? src : [];
					} else {
						clone = src && isPlainObject(src) ? src : {};
					}

					// Never move original objects, clone them
					target[name] = extend(deep, clone, copy);

				// Don't bring in undefined values
				} else if (copy !== undefined) {
					target[name] = copy;
				}
			}
		}
	}

	// Return the modified object
	return target;
};


var hasOwn = Object.prototype.hasOwnProperty;
var toString = Object.prototype.toString;
var undefined;

var isPlainObject = function isPlainObject(obj) {
	'use strict';
	if (!obj || toString.call(obj) !== '[object Object]' || obj.nodeType || obj.setInterval) {
		return false;
	}

	var has_own_constructor = hasOwn.call(obj, 'constructor');
	var has_is_property_of_method = obj.constructor && obj.constructor.prototype && hasOwn.call(obj.constructor.prototype, 'isPrototypeOf');
	// Not own constructor property must be Object
	if (obj.constructor && !has_own_constructor && !has_is_property_of_method) {
		return false;
	}

	// Own properties are enumerated firstly, so to speed up,
	// if last one is own, then all properties are own.
	var key;
	for (key in obj) {}

	return key === undefined || hasOwn.call(obj, key);
};

module.exports = function extend() {
	'use strict';
	var options, name, src, copy, copyIsArray, clone,
		target = arguments[0],
		i = 1,
		length = arguments.length,
		deep = false;

	// Handle a deep copy situation
	if (typeof target === 'boolean') {
		deep = target;
		target = arguments[1] || {};
		// skip the boolean and the target
		i = 2;
	} else if ((typeof target !== 'object' && typeof target !== 'function') || target == null) {
			target = {};
	}

	for (; i < length; ++i) {
		// Only deal with non-null/undefined values
		if ((options = arguments[i]) != null) {
			// Extend the base object
			for (name in options) {
				src = target[name];
				copy = options[name];

				// Prevent never-ending loop
				if (target === copy) {
					continue;
				}

				// Recurse if we're merging plain objects or arrays
				if (deep && copy && (isPlainObject(copy) || (copyIsArray = Array.isArray(copy)))) {
					if (copyIsArray) {
						copyIsArray = false;
						clone = src && Array.isArray(src) ? src : [];
					} else {
						clone = src && isPlainObject(src) ? src : {};
					}

					// Never move original objects, clone them
					target[name] = extend(deep, clone, copy);

				// Don't bring in undefined values
				} else if (copy !== undefined) {
					target[name] = copy;
				}
			}
		}
	}

	// Return the modified object
	return target;
};


Use == null, instead of == undefined, to be explicit about the comparison