javascript 26 lines · 5 steps

Optional chaining and nullish coalescing in JS

How ?. and ?? let you safely reach into nested objects and supply fallbacks without falsy bugs.

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Intermediate optional-chaining nullish-coalescing defensive-coding defaults short-circuit
1function getCityName(user) {
2 return user?.address?.city ?? "Unknown city";
3}
4 
5function getFirstHobby(user) {
6 return user?.profile?.hobbies?.[0] ?? "No hobbies listed";
7}
8 
9function invokeFormatter(user) {
10 return user?.settings?.formatName?.() ?? "default formatter";
11}
12 
13function resolveConfig(options) {
14 const timeout = options?.timeout ?? 3000;
15 const retries = options?.retries ?? 0;
16 const headers = options?.headers ?? {};
17 return { timeout, retries, headers };
18}
19 
20function deepValue(obj, fallback) {
21 // ?. short-circuits to undefined the moment a link is null/undefined,
22 // ?? only falls back on null or undefined (not 0, '', or false).
23 const count = obj?.stats?.count ?? fallback;
24 const isActive = obj?.flags?.active ?? false;
25 return { count, isActive };
26}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Optional chaining short-circuits to undefined the instant any link in the path is null or undefined, avoiding 'cannot read property of undefined' errors.
  2. 2Nullish coalescing only falls back on null or undefined, so legitimate values like 0, '', and false survive untouched.
  3. 3Combining ?. and ?? gives concise, safe access to deep structures with explicit defaults at the call site.

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