a problem with regex

I'm trying to clean up web pages before loading them into iframe using PHP and AJAX .

I'm trying to capture Any alert(anything can be here); promt(anything can be here); and window.location Javascript codes From HTML and .js Files bye using Below Regular Expression.

preg_replace('#^(?<alert>)(.*?)[;$]#'," ",$webpage);

it works fine only if alert(anything can be here);command exist in a line only but if there were any extra codes before this code in a same line , whole the line would be replaced with blank Space either. this is what i don't want to happen. I want Exact Part Of Code in Any Where even if there is any number of alert(anything can be here);

commands is a same line , I want them to be selected separately.

would you please help me whit that .... thank you...