// inlined jquery here, /*! jQuery v1.11.2 | (c) 2005, 2014 jQuery Foundation, Inc. | jquery.org/license */

// ...

$(document).ready(function(){

    $('.brainbox').each(function(i){

        // this works fine
        $(this).addClass('item-' + i);

        // logs ok
        console.log( i + ' is here');

        // Uncaught TypeError: Object [object Object] has no method 'getAttribute'
        console.log(  $(this).getAttribute('data-key') );