Radio button checked not recognised

I am trying to check in AMP if radio inputs are checked, but they always return undefined.

This is the html:

And this is the content of the external js file:

const button = document.getElementById('send-button');
const radioSelectedValue = document.querySelector('input[name="some-name"]');
button.addEventListener('click', () => {
console.log(radioSelectedValue.checked);
});

The console.log shows undefined.