javascript alert check

[mattfox]

I want use php to check an URL that contains some parameters, some specified parameters makes the page active an alert window.
What should i do with php?

[DrDoc]

Welcome to WebmasterWorld! [WebmasterWorld.com]

I'm not sure I entirely understand what you mean, but perhaps something like this:

<script type="text/javascript"> 
<?php 
  if(/*whatever you need to check here*/) { 
    echo "alert('foo');"; 
  } 
?> 
</script>