Open a new HTML page in a JS function and then write some HTML on it when the previous html is a login page

hi im trying to make a login page that after you push the button it goes to the index. I did that but now i want to change part of the html to say welcome back ( and the name of the username)

i’ve wrote this so far but i dont know how to save the username so i can use it again in the next page.

this is the html:

<form id="login-form">
<!--Error Message-->
        <div id="login-error-msg-holder">
      <p id="login-error-msg">Invalid username <span id="error-msg-second-line">and/or password</span></p>
    </div>

<!--Form-->
    <div class="form-floating">
      <input type="name" class="form-control name " name="name" id="floatingInput" id="name-field" placeholder="user123">
      <label for="floatingInput">Username</label>
    </div>
    <div class="form-floating">
      <input type="password" id="password-field" class="form-control" id="floatingPassword" name="password" placeholder="Password">
      <label for="floatingPassword">Password</label>
    </div>

    <div class="form-check text-start my-3">
      <input class="form-check-input" type="checkbox" value="remember-me" id="flexCheckDefault">
      <label class="form-check-label" for="flexCheckDefault">
        Remember me
      </label>
    </div>
    <button class="btn w-100 py-2" id="login-form-submit" value="Login" type="submit">Sign in</button>
    <p class="mt-5 mb-3 text-body-secondary">&copy; 2017–2024</p>
  </form>
</main>

And this is the js:

window.onload=loginButton.addEventListener("click",(e) => {
    e.preventDefault();
    const name = loginForm.name.value;
    const password = loginForm.password.value;

    if (name === "user123" && password === "1") {
        window.location.href = 'index.html';

    } else {
        loginErrorMsg.style.opacity = 1;
    }
})

function message(){

        if (window.history='Login.html' ) {
        document.getElementById('navlogin').innerHTML='Welcome back'+ name + '!';
        }
        
        else{
            document.getElementById('navlogin').innerHTML='';
        }
}

i tried using the console.log but i cant save it for a little time so i can use it later.

any ideas?