JSFiddle - React, Tailwind, and code Playground

HTML

<form action="/" method="post" onsubmit="return subimitar()">
        Usuario
        <input type="text" id="usuario" name="usuario"/>
        Senha
        <input type="text" id="senha" name="senha"/>
        <input type="submit" value="entrar"/>
    </form>

JavaScript

subimitar = function(){
        if(document.getElementById("usuario").value == ""
            ||
            document.getElementById("senha").value == ""
        ){
            alert("vocĂŞ tem que digitar os campos usuario e senha");
            return false;   
        }     
    return true;   
    }