~~~ /* let a = {n: 4}; let b = a; //=> b=AAAFFF000 =>{n:4,x:AAAFFF111} b.x = a = {n: 10}; //=>AAAFFF111 =>{n:10} //b.x=AAAFFF111 //a=AAAFFF111 =>{n:10} console.log(a.x);//=>undefined console.log(b.x);//=>{n:10} */ ~~~ ~~~ /* function C1(name) {//=>undefined if (name) this.name = name; //=>没有给实例THIS设置私有属性 } function C2(name) {//=>undefined this.name = name;//=>给实例THIS设置私有属性NAME:UNDEFINED } function C3(name) {//=>undefined this.name = name || 'join';//=>给实例THIS设置私有属性NAME:JOIN } C1.prototype.name = 'Tom'; C2.prototype.name = 'Tom'; C3.prototype.name = 'Tom'; alert(new C1().name + new C2().name + new C3().name);//=>"Tomundefinedjoin"*/ /* function C1(name) { this.name = name || 'join'; } function C2(name) { name ? this.name = name : null; } function C3(name) { this.name = name && 'join'; } C1.prototype.name = 'tom'; C2.prototype.name = 'tom'; C3.prototype.name = 'tom'; alert(new C1().name + new C2().name + new C3().name);*/ //"jointomundefined" ~~~ ~~~ let Fn = function (x = 0, y = 0) { this.x = x; this.y = y; this.getX = function () { console.log(this.x); } }; Fn.prototype.getY = function () { console.log(this.y); }; Fn.prototype = { // constructor:Fn, setX: function (val) { this.x = val; }, getX: function () { console.log(this.x); } }; let f1 = new Fn; let f2 = new Fn(1, 2); console.log(f1.constructor);//=>Object f1.setX(3);//=>this:f1 =>f1.x = 3; (把f1的私有属性改为3) [设置无输出] f1.getX();//=>this:f1 =>f1.x =>3 f1.__proto__.getX();//=>this:f1.__proto__ =>f1.__proto__.x =>undefined f1.__proto__.setX(4);//=>this:f1.__proto__ =>f1.__proto__.x = 4 给f1对应类的原型上设置x属性值为4 [设置无输出] f2.getX();//=>this:f2 =>f2.x =>1 f2.__proto__.getX();//=>this:f2.__proto__ =>f2.__proto__.x =>4 f2.getY();//=>undefined() 报错 ~~~