var url_prev;
var url_next;
var rules_prev_next= {
    crl : function(){
              url_prev = $('#btPrev').html();
              url_next = $('#btNext').html();
     }
}
$(document).ready(rules_prev_next.crl);

document.onkeydown = function(e) {
  
    var focus = null;

    try{
        focus = event.srcElement.type;
    }

    catch(err){
        focus = e.target.type;
    }

    var form_elements = new Array("text","password","select-one","textarea","button","submit");
    var activar_keydown = true;
    for(var i in form_elements){
        if(form_elements[i] == focus){
            activar_keydown = false;
            break;
        }
    }

    if(activar_keydown){
        e = (typeof e == "undefined") ? event : e;
        keyPressed = (typeof e.which == "number") ? e.which : e.keyCode;
        switch(keyPressed){
            case 37: // <--
                if(url_prev != undefined){
                    document.location.href = url_prev;
                }
                break;
            case 39:  // -->
                if(url_next != undefined){
                    document.location.href = url_next;
                }
                break;
            case 107: // +
            case 109: // -
                var tipo = 1;
                if(keyPressed == 109) tipo = -1;
                changeSize(tipo);
                break;
        }
    }
}