day019

手写题
 function compose(){
    //请实现
 }
 const multiply20 = (price) => price * 20;
 const divide100 = (price) => price / 100;
 const normalizePrice = (price) => price.toFixed(2);
 const discount = compose(normalizePrice, divide100, multiply20);
    discount(200.0); //40.00