Double question mark in Typescript & Javascript

 Double question mark in Typescript & Javascript | Nullish Coalescing (??) Operator (shareablecode.com)

Usage of ?? Sign in JavaScript and TypeScript

It returns second parameter when first parameter happens to be undefined or null. 

const value = firstParam ?? secondParam;

What's the difference between ?? and || in JavaScript / TypeScript

A common approach to achieve similar thing we use:

const value = firstParam || secondParam;

But problem is logical operator evaluates false value as well, which is not null or undefined

const foo = false
const baz = foo || 'default value'; // returns 'default value'
const value = foo ?? 'default value'// returns false;