js之类式继承，原型继承

//extend function
function extend(subClass,superClass){
  var F=function(){};
  F.prototype=superClass.prototype;
  subClass.prototype=new F();
  subClass.prototype.constructor=subClass;

  subClass.superclass=superClass.prototype;
  if(superClass.prototype.constructor == Object.prototype.constructor){
    superclass.prototype.constructor = superClass;
  }
}
//class Person
function Person(){

}

//class Author
function Author(){
  Author.superclass.constructor.call();
}
extend(Author,Person)
Author.prototype.sayName=function(){
  
};