Inheritance (the child constructor inherits the attributes in the parent constructor)

Inherit

1、call()

• call() You can call functions
• call() You can modify this The direction of , Use call() When Parameter 1 is modified this Point to , Parameters 2, Parameters 3… Use commas to separate connections

function fn(x, y) {
    
     console.log(this);
     console.log(x + y);
}
  var o = {
    
  	name: 'andy'
  };
  fn.call(o, 1, 2);// When the function is called this Point to the object o,

2. The child constructor inherits the properties in the parent constructor

1. First define a parent constructor
2. Define a sub constructor
3. The child constructor inherits the properties of the parent constructor ( Use call Method )

 // 1.  Parent constructor 
 function Father(uname, age) {
    
   // this  Object instance pointing to the parent constructor 
   this.uname = uname;
   this.age = age;
 }
  // 2 . Child constructors  
function Son(uname, age, score) {
    
  // this  Object instance pointing to the child constructor 
  3. Use call Method to realize that the child inherits the parent property 
  Father.call(this, uname, age);
  this.score = score;
}
var son = new Son(' Lau Andy ', 18, 100);
console.log(son);

3. Borrow prototype object inheritance methods

1. First define a parent constructor
2. Define a sub constructor
3. The child constructor inherits the properties of the parent constructor ( Use call Method )

// 1.  Parent constructor 
function Father(uname, age) {
    
  // this  Object instance pointing to the parent constructor 
  this.uname = uname;
  this.age = age;
}
Father.prototype.money = function() {
    
  console.log(100000);
 };
 // 2 . Child constructors  
  function Son(uname, age, score) {
    
      // this  Object instance pointing to the child constructor 
      Father.call(this, uname, age);
      this.score = score;
  }
// Son.prototype = Father.prototype;  There will be problems with direct assignment , If you modify the child prototype object , The parent prototype object changes with it 
  Son.prototype = new Father();
  //  If you modify the prototype object in the form of an object , Don't forget to use constructor  Point back to the original constructor 
  Son.prototype.constructor = Son;
  //  This is a special method for sub constructors 
  Son.prototype.exam = function() {
    
    console.log(' Children have exams ');

  }
  var son = new Son(' Lau Andy ', 18, 100);
  console.log(son);

The above code results are shown in the figure :