The nullish coalescing operator (??) is a relatively new addition to the JavaScript language (introduced in ES2020). It is a logical operator that returns the right side operand when the left side operand is null or undefined, and otherwise returns the left side operand. It is similar to the logical OR operator (||), however it checks for “nullish” values, as opposed to the broader truthy/falsy values.

There are only two “nullish” valued in Javascript – null and undefined. So the nullish coalescing operator offers a much cleaner solution for when you need to treat other falsy values as valid.

Here’s a quick example:

const foo = null ?? 'default value'; // 'default value'
const bar = 0 ?? 42; // 0 (unlike ||, which would return 42)

Further reading

You can read more about this operator on MDN.