jquery的extend函数

 var extend = (function () {

     var isObjFunc = function (name) {//返回的是一个函数
         var toString = Object.prototype.toString
         return function () {
             return toString.call(arguments[0]) === '[object ' + name + ']'//谁调用函数，就指向谁的上下文；
         }
     }

     var isObject = isObjFunc('Object'),
         isArray = isObjFunc('Array'),
         isBoolean = isObjFunc('Boolean')
       // console.log(isObject)//返回的是一个函数
       // console.log(isArray)
       // console.log(isBoolean)

     return function extend() {
         var index = 0, isDeep = false, obj, copy, destination, source, i;

         if (isBoolean(arguments[0])) {
            // console.log(isBoolean(arguments[0]))//true
             index = 1
            // console.log(arguments[0])
             isDeep = arguments[0]//ture
         }

         for (i = arguments.length - 1; i > index; i--) {//当i>1的时候，也就是参数值大于1的时候遍历
             destination = arguments[i - 1]
             source = arguments[i]
            // console.log(destination)//{name:3}
            // console.log(source)//{name:3}

             if (isObject(source) || isArray(source)) {//如果是数组或者对象；
                // console.log(source)
                 for (var property in source) {
                     obj = source[property]

                     if (isDeep && (isObject(obj) || isArray(obj))) {//如果是数组或者对象；
                         copy = isObject(obj) ? {} : []
                         var extended = extend(isDeep, copy, obj)

                         destination[property] = extended//目标的就等于深拷贝的；

                     } else {

                         destination[property] = source[property]//如果是值类型的；直接等于原来的；
                     }
                 }
             } else {//如果不是数组或者对象
                 destination = source
             }
         }
         return destination//返回目标对象
     }
 })()

 var a = {name: 1}
 var b = {name: 2}
 var c = {name: 3}
 extend(true, a, b, {name: [a, b, c], value: a})
 console.log('-----------------------')
 console.log(a)//{name:Array(3)}
 console.log(a.name[0] === a) // false
 console.log(a.value === a) // false