Open a popup box after receiving result from ajax

success: function (returndata) {
    if (returndata[4] === 1) {
        $('#bsModal3').modal(); // this
    } else {
        // other code
    }
},

$.ajax({
        type: 'post',
        url: 'test2.php',
        dataType: 'json',
        data: {
            txt: txtbox,
            hidden: hiddenTxt
        },
        cache: false,
        success: function (returndata) {
            if (returndata[4] === 1) {
               $('#bsModal3').modal();  // Please right this in your Code
            } else {
                // other code
            }
        },
        error: function () {
            console.error('Failed to process ajax !');
        }
    });