使用jQuery / Ajax和PHP显示当前进度

Short and sweet: Looking for a way to call PHP file and display the progress using jQuery and/or Ajax. PHP file upgrade.php?step=1 is called and then the output returned is appended to #upgradestatus. After that is completed upgrade.php?step=2 is called and that output is appended until the specified number of steps is completed. Looking for a way to call PHP