What do ||=, ??=, and &&= do here, including on a const?

const settings = { volume: 0, theme: "", user: null };
 
settings.volume ||= 50;
settings.theme ??= "light";
settings.user &&= settings.user.name;
console.log(settings);
 
const limit = 10;
limit ||= 20;
console.log(limit);
limit &&= 20;
console.log("done");