Optional Chaining and Nullish Coalescing

Optional chaining lets you access a nested property, call a method, or index into an array without manually checking every intermediate step for null/undefined first: user?.address?.city returns undefined immediately, short-circuiting the rest of the chain, the moment any link (user or user.address) is null or undefined, instead of throwing a TypeError like plain dot access would. The same ?. syntax works for optional method calls (obj.method?.(), which safely no-ops if method doesn't exist) and optional dynamic/array indexing (arr?.[0]).

Nullish coalescing provides a fallback value, but — unlike the logical OR operator || — it only falls back when the left-hand side is specifically null or undefined, not for other falsy values like 0, '', or false. This fixes the classic ||-based default-value bug where a legitimately falsy input (like a quantity of 0) gets incorrectly overridden by the fallback.

The two operators are frequently combined: user?.settings?.theme ?? 'light' safely traverses a potentially missing nested structure and supplies a sensible default only if the final result actually turns out to be null/undefined, rather than for any other falsy value that traversal might legitimately produce. One notable restriction: ?? cannot be directly mixed with || or && in the same expression without parentheses, since the spec considers that ambiguous and throws a SyntaxError to force the developer to be explicit about precedence.