window.location.href not working in form-html

window.location.href is not redirecting the user.
I have tried with return true also

Form Code:-

<form method="POST" name="main_form" onsubmit="login()">
<input type="email" name="email">
<input type="password" name="pwd">
<input type="submit">
</form>

Login():-

function login() {
    var email = document.main_form.email.value;
    var pwd = document.main_form.pwd.value;
    if (email == 'example@example.com' && pwd == 'example123') {
        sessionStorage.setItem("email", email);
        window.location.href = './index.html';
        return false;