JavaScript – Confirm Before Window is Closed

Here is the JavaScript code:

/** Confirms when closing the window **/

function checkClose()

{

    $("#s_scan_number").focus();

    return "Please DON'T close the window. Use the form button on the bottom.";

}

window.onbeforeunload = checkClose;

//to remove the confirmation dynamically:

window.onbeforeunload = null;