alert() is not working in js. Need help fast. Updated [closed]

no alert is coming.
I have updated the code
so you can debug it

Part of html:-

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

JS function:-

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';
    } else {
        alert('Wrong');
    }
    return false;
}