看代码学编程之js高级语法

正则

对象

function log(str) {
        if(typeof str == 'object'){
            document.write(JSON.stringify(str));

        }else {
            document.write(str);
        }

        document.write('');
    }

    try {
        var obj = {};
        obj.x = 3;
        obj.y = 5;
        function foo() {
        }

        foo.prototype.z = 3;
        var o = new foo();
        log(o.z);//3
        log(foo.hasOwnProperty('z'));//false
        obj.z = 7;
        obj.x = 7;
        log(obj.hasOwnProperty('z'));//true
        //obj.prototype.z = 5; //报错
        delete obj.z;
        log(obj.z); //undefinded
        o.z=6;
        log(o.z);//6
        delete o.z;
        log(o.z);//3
        delete o.z;//只能删除本对象的属性，不能删除原型链上的属性why？
        log(Object.getOwnPropertyDescriptor(o,"z"));//{"writable":false,"enumerable":true,"configurable":false}
        //原型链上的属性权限很低，只有可列出属性的权限，故不能删除
        Object.defineProperty(o, "z", { writable: true });
        delete o.z;//给权限以后即可删除
        log(o.z);//undefinded
        //未实例化的函数实体不具有属性描述
        log(Object.getOwnPropertyDescriptor(foo,"z"));//undefined
        log(obj.x);//7
        //自定义键值对对象的属性默认具有最高权限
        log(Object.getOwnPropertyDescriptor(obj,"x"));//{"writable":true,"enumerable":true,"configurable":true}

        Object.defineProperty(obj, "y", { writable: false });
        log(Object.getOwnPropertyDescriptor(obj,"y"));//{"value":5,"writable":false,"enumerable":true,"configurable":true}
        Object.defineProperty(obj, "y", { enumerable: false });
        log(Object.getOwnPropertyDescriptor(obj,"y"));//{"value":5,"writable":false,"enumerable":false,"configurable":true}
//        Object.defineProperty(o, "z", { enumerable: true });
        log('-----------------------------------------------------------------');

        /**
         * 对象创建
         */
        var obj1 = Object.create({x:1});
        log(obj1.x);//1
        log(Object.getOwnPropertyDescriptor(obj1,'x'));//undefinded  why?
        console.log(obj1);
        console.log(o);
        log(obj1.__proto__.constructor);//function Object() { [native code] }
        log(obj.__proto__.constructor);//function Object() { [native code] }
        log(o.__proto__.constructor);//function foo() { }
        log(obj1.hasOwnProperty('x'));//false
        //创建不带属性的空对象
        var obj2 = Object.create(null);
        console.log(obj2);//Object {}No Properties 不带任何属性
//        console.log(obj2.toString());//undefinded
        var globalVar1 =1;

        log(Object.getOwnPropertyDescriptor(window,'globalVar1'));//{"value":1,"writable":true,"enumerable":true,"configurable":false}
        log(delete globalVar);//false 特例
        globalVar2 = 2;
        log(Object.getOwnPropertyDescriptor(window,'globalVar2'));//{"value":2,"writable":true,"enumerable":true,"configurable":true}
        log(delete globalVar);//true 特例
        obj2.x=111;
        log(Object.getOwnPropertyDescriptor(obj2,'x'));//{"value":2,"writable":true,"enumerable":true,"configurable":true}
        Object.defineProperty(obj2,'x',{'writable':false});
        log(delete obj2.x);//true writable跟删除权限无关，configurable决定删除权限
        log(delete foo);//false
        (function () {
            var aa =1;
            log(delete aa);//false
        })();