JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" id="funwithforms" />
<div id="out"></div>

JavaScript

var el = document.getElementById("funwithforms"),
    gCS = getComputedStyle(el, null) || el.currentStyle,
    out = "";

out += gCS.height +" ";
out += gCS.marginTop +" ";

el.style.height = gCS.height;

out += gCS.height +" ";
out += gCS.marginTop +" ";

el.value = out;