Redirection only if the button is clicked on the previous page

I'm trying to achieve redirection only if the button is clicked on the previous page. I'm new to JS, so please be gentle.

For example:
When the users come on login page they have this button:

<button type="submit" class="form-login-submit" name="login" value="Log in">Log in</button>

When you click on Log in button you will be redirected to the My Account page which contains this class member-logged-in in body.

So, this is my code:

const logInBtn = document.querySelector('.form-login-submit');

logInBtn.addEventListener('click', () => {
  window.onload = () => document.body.classList.contains('member-logged-in') ? window.location.href = 'www.test.com' : '';
});

But when the user is redirected to the My Account page I'm getting this error, I think because the Log in button is missing on that page:

Uncaught TypeError: Cannot read property 'addEventListener' of null at (index):691

Any help is appreciated.