jQuery的实现原理的模拟代码 -4 重要的扩展函数 extend

/// <reference path="jQuery-core.js" /> 2 3 4 jQuery.extend = jQuery.fn.extend = function () { 5 // copy reference to target object 6 var target = arguments[0] || {}, i = 1, length = arguments.length, deep = false, options, name, src, copy; 7 8 // 深拷贝情况，第一个参数为 boolean 类型，那么，表示深拷贝，第二个参数为目标对象 9 if (typeof target === "boolean") { deep = target; target = arguments[1] || {}; // skip the boolean and the target i = 2; } // 如果目标不是对象也不是函数 if (typeof target !== "object" && !jQuery.isFunction(target)) { target = {}; } // 如果只有一个参数就是扩展自己 if (length === i) { target = this; --i; } // 遍历所有的参考对象，扩展到目标对象上 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 object literal values or arrays if (deep && copy && (jQuery.isPlainObject(copy) || jQuery.isArray(copy))) { var clone = src && (jQuery.isPlainObject(src) || jQuery.isArray(src)) ? src : jQuery.isArray(copy) ? [] : {}; // Never move original objects, clone them target[name] = jQuery.extend(deep, clone, copy); // Don't bring in undefined values } else if (copy !== undefined) { target[name] = copy; } } } } // Return the modified object return target; };