what does const {foo=20} = bar mean in javascript?

I couldn’t find anything to search on for this. Based on my limited testing it looks like after

const {foo = 20} = bar

foo will have the value bar.foo if it exists otherwise it will have the value 20, i.e. it’s equivalent to:

const foo = bar?.foo ?? 20

is my understanding correct?

>Solution :

No it’s not exactly equivalent.

Difference:

With ({foo = 20}), default value is used if bar.foo is undefined, but not if bar.foo is null.

const {foo = 20} = bar

With (??), the default value is used for null or undefined.

const foo = bar?.foo ?? 20

let bar = { foo: null };
const { foo = 20 } = bar;
console.log(foo); // null (not 20)

bar = { foo: null };
const fooVal = bar?.foo ?? 20;
console.log(fooVal); // 20