原型链继承

function Parent()  {
  this.name = 'parent'
}

Parent.prototype.getName = function () {
  return this.name;
}

function Child() {
  this.name = "child";
}

Child.prototype = new Parent();

var child1 = new Child();

console.log(child1.getName());// "child"

function Parent() {
  this.arr = [1,2,3];
}

//定义子类
function Child() {}

// 子类继承父类，这里是关键，实现原型链继承
Child.prototype = new Parent();

// 实例化子类
var child1 = new Child();
var child2 = new child();

child1.arr.push(4);

console.log(child1.arr)
console.log(child2.arr)