复制
1class Dog {
2  constructor(name) {
3    this.name = name;
4  }
5};
6
7class Labrador extends Dog {
8  // 1 
9  constructor(name, size) {
10    this.size = size;
11  }
12  // 2
13  constructor(name, size) {
14    super(name);
15    this.size = size;
16  }
17  // 3
18  constructor(size) {
19    super(name);
20    this.size = size;
21  }
22  // 4 
23  constructor(name, size) {
24    this.name = name;
25    this.size = size;
26  }
27
28};