null vs undefined in JavaScript: Differences, Checks and When to Use Each (Tested Examples)

undefined means a value was never assigned (missing property, missing argument, bare return ). null is an intentional empty value you assign yourself. Prefer === when you care which one you have, use == null when either should count as empty, and reach for ??

Source: [Dev.to](https://dev.to/mfaysaldev/null-vs-undefined-in-javascript-differences-checks-and-when-to-use-each-tested-examples-3k18)