I had thought someone there would give the API a try. Anyway, here's a copy and paste test from the MDN docs:
const vehicles = ['Motorcycle', 'Bus', 'Car'];
const formatter = new Intl.ListFormat('en', { style: 'long', type: 'conjunction' });
console.log(formatter.format(vehicles));
In the other major browsers, it outputs:
"Motorcycle, Bus, and Car"
In Orion, it throws:
TypeError: undefined is not a constructor (evaluating 'new Intl.ListFormat('en', { style: 'long', type: 'conjunction' })')