Super simple responsive Wordpress gallery approach

functions.php

function responsiveImages($string, $attr) {
    $output = "<div id=\"responsive-gallery-test\">";
    $posts = get_posts(array('include' => $attr['ids'], 'post_type' => 'attachment'));
    
    foreach ($posts as $image) {
        $output .= "<img data-img-small='" . wp_get_attachment_image_src($image->ID, 'thumbnail')[0] . "'" .
            " data-img-medium='" . wp_get_attachment_image_src($image->ID, 'medium')[0] . "''" .
            " data-img-large='" . wp_get_attachment_image_src($image->ID, 'large')[0] . "''" .
            " data-img-full='" . wp_get_attachment_image_src($image->ID, 'full')[0] . "'/>";
    }
    
    $output .= "</div>";
    return $output;
}

output.html

<div id="responsive-gallery-test">
    <img 
        data-img-small="/wp-content/uploads/2015/03/A-100x47.jpg" 
        data-img-medium="/wp-content/uploads/2015/03/A-300x141.jpg" 
        data-img-large="/wp-content/uploads/2015/03/A-1024x481.jpg" 
        data-img-full="/wp-content/uploads/2015/03/A.jpg" />
        
    <img 
        data-img-small="/wp-content/uploads/2015/03/B-100x47.jpg" 
        data-img-medium="/wp-content/uploads/2015/03/B-300x141.jpg" 
        data-img-large="/wp-content/uploads/2015/03/B-1024x481.jpg" 
        data-img-full="/wp-content/uploads/2015/03/B.jpg" />
</div>

setImage.js

setImageSrc($(window).width());

$(window).resize(function () {
    setImageSrc($(window).width());
});

setImageSrc setImage(width) {
    var img = null;

    if (width < 767) {
        img = 'data-img-small';
        // console.log('screen-xs');
    }

    if (width >= 768) {
        img = 'data-img-medium';
        // console.log('screen-sm');
    }

    if (width >= 992) {
        img = 'data-img-large';
        // console.log('screen-md');
    }

    if (width >= 1200) {
        img = 'data-img-full';
        // console.log('screen-lg');
    }

    $('#responsive-gallery-test').find('img').each(function() {
        this.setAttribute('src', this.getAttribute(img));
    });
}