typeof-->可以查出型別

 let a = 1 ;
 undefined
 a
 1
 typeof a  
 "number"

a的型別是"number"

let milkPrice = 30;
let milkNum = 5 ;
let totle = milkPrice * milkNum ;

totle
150

總共是150

ex:anita身上有200元，經過清心飲料店，想買飲料給家人喝，一杯無糖少冰烏龍綠茶30元，一杯無糖少冰養樂多綠茶45元，兩杯無糖少冰青茶30元，請問anita還剩多少錢？
1.anita身上有200元
2.烏龍綠茶30元
3.養樂多綠茶45元
4.青茶30元
5.烏龍綠茶一杯
6.養樂多綠茶一杯
7.青茶兩杯

let anitaMoney = 200 ;
let OolongteaPrice = 30 ;
let YakultgreenteaPrice = 45 ;
let Greenteaprice = 30 ;
let OolongteaNum = 1 ;
let YakultgreenteaNum = 1 ;
let GreenteaNum = 2 ;
let leftMoney = anitaMoney-(OolongteaPrice * OolongteaNum)-(YakultgreenteaPrice * YakultgreenteaNum)-(Greenteaprice * GreenteaNum) ;

ans:leftMoney = 65