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