# Missing Values: null, undefined, ?. and ??

Real data has holes, so learn the difference between undefined and null, read a property that might be missing with ?., and give a missing value a default with ?? instead of ||.

![Cheat sheet: Missing Values: null, undefined, ?. and ??](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/10/820059f30cb14fce92fb5f065fed0537.webp)

- Category: JavaScript
- Level: Apprentice
- Tags: JavaScript, null (javascript), Nullish Coalescing (javascript), Optional Chaining (javascript), undefined (javascript)
- Updated: November 1, 2026

Source: https://www.ask-codey.com/cheat-sheets/javascript-tricky-values-null-and-undefined-cheat-sheet