Nullish Coalescing operator ??

If left side is undefined or null then return right side

let user = null;
console.log(user ?? "Anonymous"); // Anonymous

Comparison with OR operator ||

Using OR operator is similar but working is different and could result in different behavior
If left side is false then return right side

let price = 0;
console.log(price ?? 100); // 0 since price is not undefined or null
console.log(price || 100); // 100 since price is 0 hence evaluated to false

Nullish Coalescing Assignment

Nodejs v14 does not support it, Node v16 support it

let user;
user ??= "Anonymous"; // assign Anonymous
console.log(user); // Anonymous

Optional Chaining ?.

It stops evaluation if left side is undefined or null and returns undefined

let user = {};
console.log(user?.address?.street); // undefined

More variants: ?.() and ?.[]

let dog = {
	name: 'Tommy',
	barks: function() {
		console.log('dog barks');
	}
};
 
dog.barks?.(); // dog barks
console.log(dog?.['name']); // Tommy

Combine optional chaining with null coalescing

We can use optional chaining and define a default value using null coalescing

let user = {
	address: {}
};
 
console.log(user?.address?.street ?? 'MG marg'); // MG marg