Let's learn about JavaScript object-oriented

// The obj literal creation method is similar to new Object()
// Then the obj object is an instance of Object, that is, obj.__proto__ === Object.prototype
var obj = {
  name: "fzb",
};
// So what is obj.__proto__ or Oject.prototype's __proto__? The answer is: null
console.log(obj.__proto__); // [Object: null prototype] {}
console.log(obj.__proto__.__proto__); // null

function Student(sno, name) {
  this.sno = sno;
  this.name = name;
}
const stu = new Student(201801, "fzb");

console.log(stu); // Student { sno: 201801, name: 'fzb' }
console.log(stu.__proto__); // {}
console.log(stu.__proto__.__proto__); // [Object: null prototype] {}

console.log(Student.__proto__); // {}
/* ***************The comment content will be explained in detail later***************
 * Why not Student.__proto__ = [Object: null prototype] {}
 * Because Student.__proto__ = Function.prototype 
 * Function.prototype.__proto__ = Object.prototype = [Object: null prototype] {}
 * ***************The annotation content will be explained in detail later***************
 */
console.log(Student.__proto__.__proto__); // [Object: null prototype] {}

function Person() {
  this.name = "fzb";
}

Person.prototype.running = function () {
  console.log(this.name + "Running~");
};

function Student(sno) {
  this.sno = sno;
}
Student.prototype = new Person();
// After rewriting the entire prototype object, reconfigure the constructor
Object.defineProperty(Student.prototype, "constructor", {
  configurable: true,
  enumerable: false,
  writable: true,
  value: Student,
});
Student.prototype.studying = function () {
  console.log(this.name + "Learning");
};

const stu = new Student(201801);
stu.running(); // fzb is running~
stu.studying(); // fzb is studying

// Add a little bit of code to the example above.
function Person() {
  this.name = "fzb";
  this.friends = []; // Add an attribute}
const stu1 = new Student(201801);
stu1.friends.push("zzw");
const stu2 = new Student(201801);
console.log(stu2.friends); // [ 'zzw' ]
// stu2 gets the friends attribute of stu1, which is not allowed

function Person(name) {
  this.name = name;
  this.friends = [];
}

Person.prototype.running = function () {
  console.log(this.name + "Running~");
};

function Student(sno, name) {
  Person.call(this, name); // Add code this.sno = sno;
}
Student.prototype = new Person();
// After rewriting the entire prototype object, reconfigure the constructor
Object.defineProperty(Student.prototype, "constructor", {
  configurable: true,
  enumerable: false,
  writable: true,
  value: Student,
});
Student.prototype.studying = function () {
  console.log(this.name + "Learning");
};

const stu1 = new Student(201801,"stu1");
stu1.friends.push("zzw");
const stu2 = new Student(201802,"stu2");
console.log(stu2.friends); // []