面向对象 JavaScript 中的继承

Question

我有 3 个对象，Science、Physics 和 Mathematics。

我想要最后两个对象（物理和数学） 继承Science的原型属性。

但我希望 数学 和 物理 都更新继承的属性并定义它们的属性。这已经完成，但是当我尝试通过 Physics 的实例访问 Science 属性和方法时，我不断收到 undefined。我的代码可能有什么问题。

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"],
};

第二行覆盖第一行。代码完成后，原型就是新对象。与Science 不再有任何关系，因此没有要继承的universal 属性。

您需要添加到它而不是替换prototype：

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 需要进行类似的更改。

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);