Remove Query string of css/js files

Most of the time we found that WordPress use the query string like ?ver= 2.3.7  for all the js and css files of wp-content and wp-includes files. So, when we check the performance of our site with gtmetrix.com or any other online tool, it shows some instruction to reduce that overload.

Resources with a “?” in the URL are not cached by some proxy caching servers. Remove the query string and encode the parameters into the URL for the following resources:

You can simply put the below mentioned code in your current theme’s function.php file.

function rtp_rssv_scripts() {
    global $wp_scripts;
    if (!is_a($wp_scripts, 'WP_Scripts'))
        return;
    foreach ($wp_scripts->registered as $handle => $script)
        $wp_scripts->registered[$handle]->ver = null;
}

function rtp_rssv_styles() {
    global $wp_styles;
    if (!is_a($wp_styles, 'WP_Styles'))
        return;
    foreach ($wp_styles->registered as $handle => $style)
        $wp_styles->registered[$handle]->ver = null;
}

add_action('wp_print_scripts', 'rtp_rssv_scripts', 999);
add_action('wp_print_footer_scripts', 'rtp_rssv_scripts', 999);

add_action('admin_print_styles', 'rtp_rssv_styles', 999);
add_action('wp_print_styles', 'rtp_rssv_styles', 999);

And you are done.
Clear the cache of your site/server and cross check site performance on gtmetrix.com.