You can use this plugin:
https://github.com/promatik/PHP-JS-CSS-Minifier
It uses this minifier http://javascript-minifier.com/
Or use this script from
http://javascript-minifier.com/examples
<?php
    // setup the URL, the JS and the form data
    $url = 'http://javascript-minifier.com/raw';
    $js = file_get_contents('./public/ready.js');
    $data = array(
        'input' => $js
    );
    // init the request, set some info, send it and finally close it
    $ch = curl_init($url);
    curl_setopt($ch, CURLOPT_POST, 1);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    $minified = curl_exec($ch);
    curl_close($ch);
    // output the $minified
    echo $minified;
?>
Don't forget to cache everything :)