Jquery -> vanilla javascript?

I am programmer who learning jQuery javascript but never really grasped vanilla javascript (i know I am a naughty programmer). My question is how would I go about replicating this functionality in vanilla JS?

$('select').change(function() {
    if($(this).val() == "Other (please specify)") {
        $(this).parent().parent().find("input.hidden").show();
    }
});

Answer

This site might help !

But here’s a step by step conversion:

var selects = document.getElementsByTagName('select');
for (var i=0; i<selects.length; i++) {
   selects[i].onchange = function() {
    if( this.value == "Other (please specify)") {
        var elements = this.parentNode.parentNode.getElementsByTagName("input");
        for (var j=0; j<elements.length; j++) {
           if( !elements[j].className.match(/bhiddenb/)) continue;
           elements[j].style.display = ''; // the exact thing to do here would depend on your previous actions 
        }
    }
   }
}