Elegance analysis

gistfile1.js

document.body.addEventListener('keydown', function(e) {
    ([37, 39].indexOf(e.keyCode) > -1) && pres[{37:'prev',39:'next'}[e.keyCode]]();
});

// VERSUS

document.body.addEventListener('keydown', function(e) {
    switch(e.keyCode) {
        case 37:
            pres.prev();
            break;
        case 39:
            pres.next();
            break;
        default:
            break;
    }
});