为什么我的php echo不起作用？

I'm trying to get my php file to call a function in my javascript file. After all I've read about it, it seems that the easiest way is to echo a script back like this:

echo "<script language=english> test(); </script>";

However my code does seem to work. My php file runs perfectly until the second I write an line of code with echo.

The javascript file is running on my website and the php file on my server. This is the code:

function logIn()
{
    if (window.XMLHttpRequest)
    {
        // Code for IE7+, Firefox, Chrome, Opera, Safari
        xmlhttp = new XMLHttpRequest();
    }
    else
    {
        // Code for IE6, IE5
        xmlhttp = ActiveXObject("Microsoft.XMLHTTP");
    }

    xmlhttp.open("POST", "LogIn.php", true);
    xmlhttp.send();
}

function test() {
    alert("test");
}

php file:

<?php

echo "<script language=javascript> test(); </script>";

?>

Can anyone please help me figuring out why my php file won't run when I write an echo line of code?

You are doing nothing with the response, that is why nothing is happening. Learn about onreadystatechange.