4.5sum求和

  <script>
       var arr=[{price:4,count:2},{price:5,count:3},{price:7,count:2}];
       function sum(arr){
           var total=0;
           arr.forEach(item=>{
               total=item['price']*item['count']+total
           })
           return total;
       }
       console.log(sum(arr))   //37
    </script>