使用Javascript从不同服务器上的php获取字符串

I need to make an easy JavaScript function that will out put some html to screen by calling a PHP file on a different server.

Something like this:

[JavaScript]
contents = http://www.example.com?clientID=1
print to screen contents;
[/JavaScript]

The PHP file would look up the information based on that clientID that is passed from the javascript call and then return the correct string, in this case an image.

I want to use JavaScript because I want this to be usable by everyone not just people that can add PHP to their websites, for example a basic Wordpress site wouldn't be able to include a PHP file from an outside server without an extra plugin to include the php in the page etc.

Like how you can include twitter & facebook code in your site to show your news feed but I want the server side to be PHP.

If by "different server" you mean a different domain name, then you would want to use AJAX with JSONP. JSONP prevent cross-domain issues by wrapping a JSON string with padding. I wouldn't invent a new markup unless it's absolutely necessary.

With jQuery, you would do something like this:

$.ajax({
    url: "http://www.example.com/api.php",
    dataType: "jsonp",
    success: function(data) {
        alert("JSONP Received");
   }
});

Then your server would be using PHP that would output something like this:

$data = array(
    contents => "http://www.example.com?clientID=1"
);
echo $_GET['callback'] . '(' . json_encode($data) . ')';

There are lots of examples like this. See Simple jQuery, PHP and JSONP example? and PHP, jQuery Ajax and json return over a cross domain for more information