JSFiddle - React, Tailwind, and code Playground

HTML

<input class="textbox" />

JavaScript

function addEvent(obj, evType, fn, useCapture){
    if (obj.addEventListener){
        obj.addEventListener(evType, fn, useCapture);
        return true;
    } else if (obj.attachEvent){
        var r = obj.attachEvent("on"+evType, function() {
            return fn.apply(obj, arguments);
        });
        return r;
    } else {
        alert("Handler could not be attached");
    }
} 

window.onload = initForm;
function initForm() {
    var allTags = document.getElementsByTagName("*");
    for(i=0; i<allTags.length; i++) {
        if (allTags[i].className.indexOf("textbox") > -1) {
            addEvent(allTags[i], "focus", fieldSelect);
            addEvent(allTags[i], "blur", fieldDeSelect);          
        }
    }
}
function fieldSelect() {
    this.style.background = "#abcdef";
}

function fieldDeSelect() {
    this.style.background = "#ccc";
}