<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css"> <script src="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script> <script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script> <!------ Include the above in your HEAD tag ----------> var ary=[1,2,3,4,5,6,7,8,9,10] function fun(a,b){ var sum=0; for(var i=0;i<ary.length;i++){ if(i>=a&&i<=b) sum+=ary[i]; } console.log(sum); }