How to dynamically call a php function in javascript

Question

I have an index.php with the following js function:

function returnImageString() {
    return "<?php include 'inc/image.functions.php'; echo getRandomImages(7); ?>";        //This isn't dynamic; this will always return the same images.  How do I fix this?
}

However, when the page loads, the php script is called and the result is added to the source code like this:

function returnImageString() {
    return "images/20.11.A1B9.jpg|images/8.14.47683.jpg|images/19.10.FBB9.jpg|images/21.12.9A.jpg|images/8.11.1474937909.jpg|images/8.15.99404.jpg|images/8.10.jpg|"; //This isn't dynamic; this will always return the same images. How do I fix this?
 }

What I want to happen is whenever I call the js function (returnImageString), I want it to call the php function each time (since the php function returns a string of random image locations) instead of having the string hardcoded in the js function.

Can someone point me in the right direction? Thanks!

Answer 1

This is not possible because you're mixing client-side behavior with server-side behavior. What you need to do is create an AJAX request to the server.

If you were using a library like jQuery (which you really want to, because it makes AJAX a breeze) you would do something like this:

PHP Code (maybe randomImages.php?)

// query for all images
// $_GET['limit'] will have the limit of images
// since we passed it from the Javascript
// put them all in an array like this:
$images = array('images/20.11.A1B9.jpg','images/20.11.A1B9.jpg',...);
print json_encode($images); // return them to the client in JSON format.
exit;

Client Side Javascript

function getRandomImages(limit) {
    // make request to the server
    $.getJSON('/path/to/randomImages.php', {limit: limit}, function(data) {
        // data is now an array with all the images
        $.each(data, function(i) {
            // do something with each image
            // data[i] will have the image path
        });
    });
}

Alternatively, if the amount of images is finite, you can skip all this crazyness and simply have an array with all the images and generate 8 random ones from the Javascript itself. This would probably be better for smaller data sets and even some bigger ones.