es6 super关键字的理解与应用实例分析

class A {
 constructor() {
  console.log(new.target.name);
 }
}
class B extends A {
 constructor() {
  super();//这里的super相当于A类的constructor构造函数，会执行A的constructor,此时的this指
      //向的是B,所以打印出B
      //换一种方法理解是在执行super时，A把constructor方法给了B，此时B有了A的功能，执
      //行的是B的内容，也就是es5的A.prototype.constructor.call(this)。
 }
}
new A() // A
new B() // B

class A {
 constructor() {
  this.x = 1;
 }
 print() {
  console.log(this.x);
 }
}
class B extends A {
 constructor() {
  super();
  this.x = 2;
 }
 m() {
  super.print();
 }
}
let b = new B();
b.m() // 2

class Parent {
 static myMethod(msg) {
  console.log('static', msg);
 }
 myMethod(msg) {
  console.log('instance', msg);
 }
}
class Child extends Parent {
 static myMethod(msg) {
  super.myMethod(msg);
 }
 myMethod(msg) {
  super.myMethod(msg);
 }
}
Child.myMethod(1); // static 1
var child = new Child();
child.myMethod(2); // instance 2