How and why would I write a class that extends null?

Question

JavaScript\'s class syntax, added in ES6, apparently makes it legal to extend null:

class foo extends null {}

Some Googling reveals that it was

Answer 1

To answer the second part:

I can't make much sense of this hypothetical use case.

That way, your object won't have Object.prototype in its prototype chain.

class Hash extends null {}
var o = {};
var hash = new Hash;
o["foo"] = 5;
hash["foo"] = 5;
// both are used as hash maps (or use `Map`).
hash["toString"]; // undefined
o["toString"]; // function

As we know, undefined in fact is not a function. In this case we can create objects without fearing a call on a field that shouldn't be there.

This is a common pattern through Object.create(null) and is common in a lot of code bases including big ones like NodeJS.