show_alert_dialog.js

function showAlertDialog() {
    var alertStrings = {
        confirmButtonLabel: "This is text shown on the confirmation button",
        text: "This is text shown on the dialog"
    };
    var alertOptions = {
        height: 200,
        width: 400
    };

    Xrm.Navigation.openAlertDialog(alertStrings, alertOptions).then(
        result => {
            console.log("Success! The dialog was shown");
        },
        error => {
            concole.log(error.message);
        }
    );
}