function Animal(name,weight){
   this.name = name;
   this.weight = weight;
}
 
function Cat(){
    Animal.call(this,'cat','50');
  //Animal.apply(this,['cat','50']);
 
   this.say = function(){
      console.log("I am " + this.name+",my weight is " + this.weight);
   }
}
 
var cat = new Cat();
cat.say();//I am cat,my weight is 50

call（）實現(xiàn)繼承的原理我動，但是上面這段代碼cat直接調(diào)用say()的話不應(yīng)該是只執(zhí)行Cat構(gòu)造函數(shù)里的say方法嗎？而Animal.call(this,'cat','50');這一行不應(yīng)該沒執(zhí)行嗎？難道是因為new一個cat實例的時候會把Cat函數(shù)先執(zhí)行一遍么？求解