Cannot implicitly convert type 'void' to 'object'

Question

In my HomeController.cs I set Session:

public IActionResult Index(Mod m)
{
    if (m.Password == "1234")
    {
        HttpContext.Session.SetString("Login", "True");
        ViewBag.Login = "True";
    }
    ...
}

and I want to change Session values in JavaScript:

...
<input type="submit" value="Login" asp-for="Login" />

<a href="#" id="submit-link" class="button" onclick="submit();">Logout</a>
...

<script type="text/javascript">
    function submit() {
        var v = '@Context.Session.GetString("Login")';
        alert(v);
        '@Context.Session.SetString("Login", "False")'; // ERROR --> Cannot implicitly convert type 'void' to 'object'
    }
</script>

Session.GetString works fine, but Session.SetString has error. I dont't know how to convert void to object here.