I have a form with a submit button. I can not change it and anything about the html.

<form>
  <input type="text" class="form-control" id="username" required />
  <label for="username">Username</label>
  <input type="password" class="form-control" id="password" required />
  <label for="password">Password</label>
  <button id="submit" class="btn btn-lg" type="submit">Sign in</button>
  <form></form>
</form>

This is my js:

let nombre = document.getElementById("username").value;
let pass = document.getElementById("password").value;

async function login() {
  try {
    const response = await fetch("http://localhost:8888/login", {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
      },
      body: JSON.stringify({ username: nombre, password: pass }),
    });
    if (response.status !== 200) throw response.statusText;
    const content = await response.json();
    return content;
  } catch (error) {
    console.log("Errorr:" + error);
  }
}

function submit() {
  let validacion1 = document.getElementById("username").checkValidity();
  let validacion2 = document.getElementById("pass").checkValidity();
  if (validacion1 == true && validacion2 == true) {
    login();
  }
}

document.getElementById("submit").addEventListener("click", submit);

But if I click on my submit button, the page "recharge" and I can not do the login properly.

I should click the submit button and wait for the username and password to be correct.

How can I click the submit button and not instantly recharge the page?

Thank you so much