我正在尝试构建用于学习目的的购物车。我有以下代码HTMLjsvarcart=(function(){cart.createCart=function(cartId){console.log(cartId);cartId=document.getElementById(cartId);}returncart;}());varshoopingCart=cart.createCart("MyCart");但是这段代码抛出以下错误UncaughtTypeError:Cannotsetproperty'createCart'ofundefined在互联网上花了几个小时并遵循了一些教程后，我对代码

Customer(cid,cname,caddress,ccity,cstate,czip,ccardnum)Product(pid,pname,pbrand,pprice)ShoppingCart(cartid,cid,active,totalprice)ShoppingCart.cidreferencestoCustomer.cidCartItem(cartid,pid,iprice,iquantity)CartItem.cartidreferencesShoppingCart.cartid,CartId.pidreferencesProduct.pidOrder(oid,cart