JSFiddle - React, Tailwind, and code Playground

HTML

<div><span id="largura"></span>x<span id="altura"></span></div>

JavaScript

window.onresize=function() {
    getDimensions()
}

function getDimensions() {
    var largura = document.getElementById('largura'),
        altura = document.getElementById('altura');
    
    largura.innerText = window.innerWidth;
    altura.innerText = window.innerHeight;
}

getDimensions();