I'm trying to use this data validation code using JavaScript from the freeCodeCamp website to implement into my code, but when I test the code itself in vscode using a live browser, it doesn't work, but works well in jsfiddle. I'm not sure why it doesn't work well in a browser?

freeCodeCamp article i got it from:https://www.freecodecamp.org/news/form-validation-with-html5-and-javascript/

freeCodeCamp jsfiddle code https://jsfiddle.net/0tq3e49w/4/

Html code:

<form id="form">
  <label for="firstname"> First Name* </label>
  <input type="text" name="firstname" id="firstname" />
  <button id="submit">Submit</button>

  <span role="alert" id="nameError" aria-hidden="true">
    Please enter First Name
  </span>
</form>

JS code:

const submit = document.getElementById("submit");

submit.addEventListener("click", validate);

function validate(e) {
  e.preventDefault();

  const firstNameField = document.getElementById("firstname");
  let valid = true;

  if (!firstNameField.value) {
    const nameError = document.getElementById("nameError");
    nameError.classList.add("visible");
    firstNameField.classList.add("invalid");
    nameError.setAttribute("aria-hidden", false);
    nameError.setAttribute("aria-invalid", true);
  }
  return valid;
}

CSS code:

#nameError {
  display: none;
  font-size: 0.8em;
}

#nameError.visible {
  display: block;
}

input.invalid {
  border-color: red;
}