const firstName = (message
&& message.body.user.firstName) || 'default';
to become code that looks like
const firstName = message.body?.user?.firstname || 'default';
The proposal is now in stage 1 which means that TC39 “expects to devote time to examining the problem space, solutions and cross-cutting concerns”. It’s still early to get excited about this, but this is one of those pieces of syntactical sugar that make writing code easier.