面向对象 JavaScript 中的继承

Question

我有 3 个对象：科学、物理和数学。

我希望最后两个对象（物理和数学） 继承科学的原型属性。

然而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实例访问Science属性和方法时，我总是得到未定义的信息。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"],};第二行将覆盖第一行。代码完成后，原型就是新对象。与 不再有任何关系Science，因此没有universal财产可以继承。您不需要替换prototype，而是需要添加：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将需要类似的改变。function log(elem) {  return console.log(elem);}//create supertype => Sciencefunction Science() {}//define Science prototype propsScience.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 Sciencefunction Mathematics(subField) {  this.subField = subField;}function Physics() {}//let mathematics & Physics inherit science propsMathematics.prototype = Object.create(Science.prototype);Physics.prototype = Object.create(Science.prototype);Physics.prototype.constructor = Physics;//over write Mathematics inherited props and physicsObject.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 Physicslet mechanics = new Physics();mechanics.name = "mechanics";mechanics.subFields = ["linear", "force", "force fileds"];log(mechanics.universal);