Accessing ProductOptions in text box

Hopefully I’m doing something silly here out of being new, but I’m a little stumped. I want to display product option details in a text box. So, simply “Size: M” without it being a dropdown.

This is fine:

product = await $w( ‘#productPage1’ ).getProduct();
let productName = product dot name;
$w( ‘#text21’ ).text=productName;

This kicks up the error below:

product = await $w( ‘#productPage1’ ).getProduct();
let size = product dot productOptions dot size dot value;
$w( ‘#text20’ ) dot text=size;

TypeError: Cannot read property ‘value’ of undefined

I would expect the output to simply be “M”, or whatever size as appropriate. What do I have to do to access that info and display it as text?

Any answers appreciated! (Apologies for the “dot” rather than punctuation, I’m too new to post links and that seems to be the cause of it.)