extend.js

'use strict';

var hasOwn = Object.prototype.hasOwnProperty;
var toStr = Object.prototype.toString;
var defineProperty = Object.defineProperty;
var gOPD = Object.getOwnPropertyDescriptor;

var isArray = function isArray(arr) {
	if (typeof Array.isArray === 'function') return Array.isArray(arr);
	return toStr.call(arr) === '[object Array]';
};
var isPlainObject = function isPlainObject(obj) {
	if (!obj || toStr.call(obj) !== '[object Object]') return false;
	var hasOwnConstructor = hasOwn.call(obj, 'constructor');
	var hasIsPrototypeOf = obj.constructor && obj.constructor.prototype && hasOwn.call(obj.constructor.prototype, 'isPrototypeOf');
	if (obj.constructor && !hasOwnConstructor && !hasIsPrototypeOf) return false;
	var key;
	for (key in obj) { /**/ }
	return typeof key === 'undefined' || hasOwn.call(obj, key);
};
var setProperty = function setProperty(target, options) {
	var check = Object.getOwnPropertyDescriptor(target, options.name);
	if (!!check && !!check.get) return;
	if (defineProperty && options.name === '__proto__') {
		defineProperty(target, options.name, {
			enumerable: true,
			configurable: true,
			value: options.newValue,
			writable: true
		});
	} else {
		target[options.name] = options.newValue;
	}
};
var getProperty = function getProperty(obj, name) {
	if (name === '__proto__') {
		if (!hasOwn.call(obj, name)) {
			return void 0;
		} else if (gOPD) {
			return gOPD(obj, name).value;
		}
	}
	return obj[name];
};

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

	if (typeof target === 'boolean') {
		deep = target;
		target = arguments[1] || {};
		i = 2;
	}
	if (target == null || (typeof target !== 'object' && typeof target !== 'function')) target = {};
	for (; i < length; ++i) {
		options = arguments[i];
		if (options != null) {
			for (name in options) {
				src = getProperty(target, name);
				copy = getProperty(options, name);
				if (target !== copy) {
					if (deep && copy && (isPlainObject(copy) || (copyIsArray = isArray(copy)))) {
						if (copyIsArray) {
							copyIsArray = false;
							clone = src && isArray(src) ? src : [];
						} else {
							clone = src && isPlainObject(src) ? src : {};
						}
						setProperty(target, { name: name, newValue: extend(deep, clone, copy) });
					} else if (typeof copy !== 'undefined') {
						setProperty(target, { name: name, newValue: copy });
					}
				}
			}
		}
	}
	return target;
};