JSFiddle - React, Tailwind, and code Playground

HTML

<html>
<input type="hidden" name="_task" value="login">
<input type="hidden" name="_action" value="login">
<input type="hidden" name="_timezone" id="rcmlogintz" value="_default_"><input type="hidden" name="_url" id="rcmloginurl" value="">
<table>
  <tbody>
    <tr>
      <td class="title">
        <label for="rcmloginuser">Username</label>
      </td>
      <td class="input">
        <input name="_user" id="rcmloginuser" required="required" size="40" autocapitalize="off" autocomplete="off" type="text">
      </td>
    </tr>
    <tr>
      <td class="title">
        <label for="rcmloginpwd">Password</label>
      </td>
      <td class="input">
        <input name="_pass" id="rcmloginpwd" required="required" size="40" autocapitalize="off" autocomplete="off" type="password">         </td>
    </tr>
    </tbody>
    </table>
    </html>

JavaScript

document.getElementById("rcmloginuser").placeholder = "Placeholder";
document.getElementById("rcmloginpwd").setAttribute("placeholder", "Password");