Displaying Attachment's Count in Separate Column using Javascript/Ajax

Hello All,

i done the Count Attachment's in SPList and storing the count value in separate column. The problem is when in list we cross the 100 itmes , the list  page takes more time for loading and list page is getting error .

And my actual list is contains 1000 items .

Below is the code i used ,please check and upadate the code for better  page performance.Please help me.

<script type="text/javascript" src="/Style%20Library/jquery-1.12.0.min.js"></script><script type="text/javascript">
$(document).ready(function () {

 getListItems();




});

function getListItems()
{

$.ajax({
        url: "Https://www.example.com" + "/_api/web/lists/getbytitle('ListName')/items",
        method: "GET",
        headers: { "Accept": "application/json; odata=verbose" },
        success: function (data) {
            for (var i = 0; i < data.d.results.length; i++) {
            //console.log(data.d.results[i]);
            var itemscount = getattachments(data.d.results[i].ID);
            console.log(itemscount)
            function getItemTypeForListName(name) {
                return "SP.Data." + name.charAt(0).toUpperCase() + name.slice(1) + "ListItem";
            }

            var item = {
                        "__metadata": { "type":  getItemTypeForListName("Listname")  },
                        "AttachmentCount": itemscount
                       };
        $.ajax({
            url: data.d.results[i].__metadata.uri,
            type: "POST",
            contentType: "application/json;odata=verbose",
            data: JSON.stringify(item),
            headers: {
                "Accept": "application/json;odata=verbose",
                "X-RequestDigest": $("#__REQUESTDIGEST").val(),
                "X-HTTP-Method": "MERGE",
                "If-Match": "*"
            },
            success: function (data) {
                console.log("Success");
            },
            error: function (data) {
                console.log("Fail");
            }
        });

        }

        },
        error: function (data) {
            failure(data);
        }
    });


}

function getattachments(itemid)
{
var url = "https://www.example.com" + "/_api/web/lists/getbytitle('listname')/items(" + itemid + ")/AttachmentFiles";
var itemscount;
$.ajax({

    url: url,
    headers: {
                "Accept": "application/json; odata=verbose"
            },
    method: "GET",
    async: false,
    success: onQuerySuccess,
    error: onQueryError
});



function onQuerySuccess(data) {

    if (data) {
        //console.log(data.d.results.length);
        var items = data.d.results;
        itemscount = data.d.results.length;

        for (var i = 0; i < items.length; i++) {
            //console.log(items[i].FileName);
        }

    }
}

function onQueryError(error) {
    attCount =0;
    alert(error.statusText);
}

return itemscount;}
</script>

Thanks in Advance.                                          

Regards,

Santto