面向对象JavaScript中的继承

Question

我有三个对象，Science，物理和数学。

我希望最后两个对象( Mathematics__)、__、、物理、和)继承Science的原型属性。

然而，我希望数学和物理都能更新继承的属性并定义它们。这已经完成了，但是当我试图通过物理实例访问科学属性和方法时，我一直得到未定义的。我的密码可能有什么问题。

​

function log(elem) {
  return console.log(elem);
}
//create supertype => Science
function Science() {}

//define Science prototype props
Science.prototype = {
  constructor: Science,
  dificulty: "Variable",
  universal: true,
  type: "science",
  name: "science",
  hasSubFields() {
    return true;
  },
};

//create 2 sub fields : Mathematics and Physics to inherit props from Science
function Mathematics(subField) {
  this.subField = subField;
}
function Physics() {}

//let mathematics & Physics inherit science props
Mathematics.prototype = 
Object.create(Science.prototype);
Physics.prototype = 
Object.create(Science.prototype);
Physics.prototype.constructor = Physics;

//over write Mathematics inherited props and physics
Mathematics.prototype = {
  constructor: Mathematics,
  name: "Mathematics",
  type: "Pure and applied Science",
};

Physics.prototype = {
  name: "Physics",
  dificulty: "80%",
  type: "Physical Science",
  subFields: ["Electricity", "Mechanics", "Sound", "Optics", "Waves"],
};

//make instance of Physics
let mechanics = new Physics();
mechanics.name = "mechanics";
mechanics.subFields = ["linear", "force", "force fileds"];

log(mechanics.universal);

​

Answer 1

Physics.prototype = new Science();

//...

Physics.prototype = {
  name: "Physics",
  dificulty: "80%",
  type: "Physical Science",
  subFields: ["Electricity", "Mechanics", "Sound", "Optics", "Waves"],
};

第二行是覆盖第一行。一旦代码完成，原型就是新的对象。不再存在与Science的任何关系，因此没有universal属性可继承。

与其替换prototype，还需要添加以下内容：

Physics.prototype = new Science();

//...

Physics.prototype.name = "Physics";
Physics.prototype.dificulty = "80%";
Physics.prototype.subFields = "Physical Science";
Physics.prototype.name = ["Electricity", "Mechanics", "Sound", "Optics", "Waves"];

或者：

Physics.prototype = new Science();

//...

Object.assign(Physics.prototype, {
  name: "Physics",
  dificulty: "80%",
  type: "Physical Science",
  subFields: ["Electricity", "Mechanics", "Sound", "Optics", "Waves"],
});

Mathematics将需要类似的更改。

​

function log(elem) {
  return console.log(elem);
}
//create supertype => Science
function Science() {}

//define Science prototype props
Science.prototype = {
  constructor: Science,
  dificulty: "Variable",
  universal: true,
  type: "science",
  name: "science",
  hasSubFields() {
    return true;
  },
};

//create 2 sub fields : Mathematics and Physics to inherit props from Science
function Mathematics(subField) {
  this.subField = subField;
}
function Physics() {}

//let mathematics & Physics inherit science props
Mathematics.prototype = Object.create(Science.prototype);
Physics.prototype = Object.create(Science.prototype);
Physics.prototype.constructor = Physics;

//over write Mathematics inherited props and physics
Object.assign(Mathematics.prototype, {
  constructor: Mathematics,
  name: "Mathematics",
  type: "Pure and applied Science",
});

Object.assign(Physics.prototype, {
  name: "Physics",
  dificulty: "80%",
  type: "Physical Science",
  subFields: ["Electricity", "Mechanics", "Sound", "Optics", "Waves"],
})

//make instance of Physics
let mechanics = new Physics();
mechanics.name = "mechanics";
mechanics.subFields = ["linear", "force", "force fileds"];

log(mechanics.universal);

​