How to add multiple item in paginit clientscript

My problem is the last item from PO is always overwrite the first added item. Here my snipped code. thank you in advance

User Event

function beforeLoad(context) {
    // try {
    if (context.type == context.UserEventType.VIEW) {


        var objPORec = context.newRecord;
        var parentPOId = objPORec.id;
        var form = context.form;


        //Add Client Script File
        form.clientScriptModulePath = './po_bill_btn.js'
        form.addButton({
            id: 'custpage_create_child_so',
            label: 'Create Vendor Bill',
            functionName: 'vendorBillFunc("' + parentPOId + '")'
        });
    }
}

clientscript

function init(context) {
    currentRecord = context.currentRecord;

    var items = [{ "item_display": "3247", "quantity": 1 }, { "item_display": "3247", "quantity": 1 }];
    for (var x = 0; x < items.length; x++) {
        addVendorBillLine(items, x);
    }
}

function addVendorBillLine(itemList, x) {
    currentRecord.selectNewLine({
        sublistId: 'item'
    });
    currentRecord.setCurrentSublistText({
        sublistId: 'item',
        fieldId: 'item',