Use of bootstrap affix

Why 80% of the code can not do farming architect? >>>  

bootstrap affix

<div class="js-affix">

sidebar

</div>

Configuring css

.js-affix {
    top: 10px;
}

.js-affix.affix-bottom {
    position: absolute;
}

js

$('.js-affix').affix({
    offset: {
        top: 112,
        bottom: 434
    }
});

Reproduced in: https: //my.oschina.net/lemos/blog/3058983