Loading JavaScript

simple

var oScript = document.createElement('script');
oScript.src = 'URL';
document.head.appendChild(oScript);

with callback

var oScript = document.createElement('script');
oScript.onload = function () {
    // ...code...
};
oScript.src = 'URL';
document.head.appendChild(oScript);

Loading CSS

var oLink  = document.createElement('link');
oLink.id   = cssId;
oLink.rel  = 'stylesheet';
oLink.type = 'text/css';
 […]

say you want to sort the following array by the value of mainType.

array $aData

$aData = array(
    0 => array(
        'name' => 'abc',
        'size' => 7000,
        'type' => 'image/png',
        'mainType' => 'image',
    ),
    1 => array(
        'name' => 'document',
        'size' => 25000,
        'type' => 'application/pdf',
        'mainType' => 'application',
    )
);

sort method
using php's usort command here will do the job.

 […]