WP_Query results stored in variables

From what I read, you read the URL/path to the post thumbnails is an array. We need to look at a couple of things here to make this as lean and predictable as possible

IMPORTANT CONSIDERATIONS

• We do need some way to make sure that we get the latest three posts which actually have thumbnails to avoid unexpected output and bugs. It is always important to code with a mindset that my code will be hacked and it will fail and it will have bugs. Once you have that mindset, then you look at your code from a different angle, which make you to ask questions like: What if this specific poece of code returns an error, how will it affect my output, how will I handle such errors safely and reliable in an expected, predictable way without breaking something else on my site

• We only really need the post ID’s from the three latest posts, so to save resources, why not only query for post ID’s

• When you need lean, non-paginated, to the point queries like this, I always use get_posts as it breaks pagination legally. This makes your query faster, which really helps on sites with many posts. You can still use WP_Query, but then you would need to remember to pass 'no_found_rows' => true to your query arguments (which is exactly what get_posts does btw). Another plus using get_posts is that it just return the $posts property from the WP_Query instance. But this is all just personal preference

THE CODE

I prefer to write functions for long pieces of code to keep my templates as simple and short as poosible. I can then just call my functions where I need them or even use do_action() calls in my templates and then hook my functions to that specific action

Anyway, lets look at the function; (NOTE: The following is untested, needs PHP 5.4+ and canbe made more dynamic as needed)

function get_latest_post_thumbnails_urls()
{
    // Set an empty variable which will hold our array of URL's
    $output = [];

    // Set our query args
    $args = [
        'posts_per_page' => 3,
        'fields'         => 'ids', // Only get post ID's
        'meta_query'     => [ // Get posts which has thumbnails only
            [
                'key'     => '_thumbnail_id',
                'compare' => 'EXISTS'
            ]
        ],
        // Any additional parameters you might need
    ];
    $q = get_posts( $args );

    // ALWAYS make sure we have posts, else return $output
    if ( !$q )
        return $output;

    // Ok, we have posts, lets loop through them and create an array of URL's
    foreach ( $q as $id ) 
        $output[] = wp_get_attachment_url( get_post_thumbnail_id( $id ) );

    // Return our array
    return $output;
}

We can now use get_latest_post_thumbnails_urls(); anywhere where we need it.

USAGE

We need to remember, our function might return an empty array, or an array with 1, 2, or 3 URL’s, so we must always make sure about this before we try to use anything to avoid bugs and have unexpected failures

This is a probable safe usecase we can use

$urls = get_latest_post_thumbnails_urls();
// Make sure we do not have an empty array

if ( $urls ) {
    foreach ( $urls as $url ) {
        // Do something with your thumbnail url
        echo $url . '</br>'; // For testing, remove this
    }
}