javascript - javascript 中的继承不起作用

Question

为什么jordan没有Human类的属性？难道说 Coder.prototype = new Human; 就足以让所有 Coder 类继承 Human 类的所有属性吗？

这与将函数定义为赋值有什么关系吗？

var Human = function() {
     var hi = function() {
         alert('hi');
      };
     return {
        name : 'dan',
       sayHi : hi
     };
};

var dan = new Human();

var Coder = function() {
   var code = function() {
      alert('1010101');
   };    
  return {
    code : code
  };
};

Coder.prototype = new Human;
Coder.prototype.constructor = new Coder;
var jordan = new Coder();
console.log(jordan);

Answer 1

您的构造函数不会返回它们正在创建的对象，因此继承不起作用。改用这个:

var Human = function() {
     this.sayHi = function() {
         alert('hi');
     };
     this.name = 'dan';
};

var dan = new Human();

var Coder = function() {
   this.code = function() {
      alert('1010101');
   };    
};

Coder.prototype = new Human;
Coder.prototype.constructor = Coder;
var jordan = new Coder();
console.log(jordan);

另一种选择，将内容从 Human 移至原型(prototype):

var Human = function() {};
Human.prototype.sayHi = function() {
    alert('hi');
};
Human.prototype.name = 'dan'; // will be shadowed if redefined on instances

var Coder = function() {};
Coder.prototype = Object.create(Human.prototype);
Coder.prototype.code = function() {
    alert('1010101');
};  
var jordan = new Coder();
console.log(jordan);

Object.create 的 polyfill 是 available on MDN