why is this recursive catch sometimes being undefined for thethen parameter?

When you recursively call responseToTom() from the .catch() handler, you are relying on the fact that responseToTom() will return a promise that resolves to a value. But, in this code:

    .then((greet) => {
        if (greet == undefined){
          console.error("Ups undefined")
        }
        console.log(greet)
    });

You aren’t returning any value so that will always resolve to an undefined value. You probably want to add return greet to that .then() handler.