System Design: Bloom Filters
Size a Bloom filter from item count and target error rate, see why it never gives false negatives, and know when it's the wrong tool.
~8 min readread →
Developer interview notes & guides — Page 2
Focused explanations and longer guides, with worked scenarios, common mistakes and interview exercises across every chapter.
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Showing 25–48 of 200 articles
System Design: Presence Tracking
Build online indicators for 10 million users: heartbeats with TTLs, why the TTL must cover lost beats, and fan-out only to who's watching.
~7 min readread →
System Design: Time-Series Metrics
Design a metrics store: count series before samples, keep labels bounded, roll up with retention tiers, and never average percentiles.
~7 min readread →
System Design: URL Shortener
Size a URL shortener from 100M links a month, pick between counter-based and random codes, and keep a 4,000 req/s redirect path cheap.
~7 min readread →
TypeScript Abstract Classes: What They Enforce and When
What TypeScript's abstract keyword enforces, why it vanishes at runtime, and when a template-method base class beats an interface.
~7 min readread →
TypeScript Declaration Files and Untyped Packages
Write a .d.ts for an untyped CommonJS package, pick export = or export default, augment globals, and ship your own types correctly.
~7 min readread →
TypeScript Enums vs Union Types
What TypeScript enums compile to, why string enums reject plain strings from JSON, and when an as const object beats both options.
~6 min readread →
TypeScript Generic Defaults and Parameter Order
How TypeScript type parameter defaults interact with inference, why one explicit type argument switches inference off, and how to order them.
~6 min readread →
TypeScript Index Signatures and Constraints
How index signatures constrain every property, why reads skip undefined until noUncheckedIndexedAccess, and when Record or Map fits better.
~6 min readread →
TypeScript Key Remapping in Mapped Types
Rename keys with as clauses, drop keys by mapping to never, map over a union of events, and spot the string & K and optional-method traps.
~6 min readread →
TypeScript Template Literal Types
Build string types from unions, parse route parameters with infer, see what ${number} really accepts, and know where these types stop helping.
~6 min readread →
Can't bind to 'ngModel' since it isn't a known property of 'input' in Angular
Fix Angular NG8002 Can't bind to 'ngModel' since it isn't a known property of 'input': import FormsModule, then fix formControl and inputs.
~7 min readread →
Angular 'Blocked by CORS Policy' on ng serve: Fix with proxy.conf.json
Fix 'blocked by CORS policy' errors when Angular ng serve calls a backend: proxy.conf.json, angular.json wiring and production CORS setup.
~8 min readread →
ExpressionChangedAfterItHasBeenCheckedError in Angular (NG0100)
Fix Angular NG0100 ExpressionChangedAfterItHasBeenCheckedError: why the dev-mode check fires, and data-flow fixes that beat setTimeout.
~8 min readread →
'app-x' is not a known element in Angular (NG8001): How to Fix It
Fix Angular NG8001 'app-x' is not a known element: standalone imports, selector typos, NgModule exports, schemas and TestBed setup.
~7 min readread →
NullInjectorError: No provider for X! in Angular (NG0201): How to Fix
Fix Angular NullInjectorError: No provider for X! (NG0201): read the injector path, add provideHttpClient(), providedIn root or a token.
~8 min readread →
Docker 'exec format error': When the Image CPU Does Not Match
Fix 'exec format error' in Docker: confirm the CPU architecture mismatch with uname and docker inspect, then rebuild with the right --platform or buildx target.
~9 min readread →
Docker 'Bind for 0.0.0.0:8080 failed: port is already allocated' Fix
Fix Docker 'port is already allocated' and 'address already in use': find the container or process on the port, then remap or bind to 127.0.0.1.
~8 min readread →
Git: Your branch and 'origin/main' have diverged (Fix)
Fix 'Your branch and origin/main have diverged' and fatal: Need to specify how to reconcile divergent branches: merge, rebase or ff-only.
~7 min readread →
Git: failed to push some refs (fetch first, non-fast-forward)
Fix Git's error: failed to push some refs and ! [rejected] main -> main (fetch first): fetch, rebase or merge, and force-with-lease safely.
~7 min readread →
Git fatal: refusing to merge unrelated histories (How to Fix)
Fix Git's fatal: refusing to merge unrelated histories: why it happens, when --allow-unrelated-histories is right, and safer alternatives.
~8 min readread →
ClassNotFoundException vs NoClassDefFoundError in Java
ClassNotFoundException vs NoClassDefFoundError in Java: what each error means, why classes go missing at runtime and how to fix the classpath.
~8 min readread →
Java ConcurrentModificationException: Removing Items Safely
Fix java.util.ConcurrentModificationException when removing items in a loop: use removeIf or Iterator.remove, and see when concurrent lists help.
~7 min readread →
Java NullPointerException: Reading the Message and Fixing the Cause
Fix java.lang.NullPointerException by reading the helpful message, finding the null in the top stack frame and validating inputs early.
~8 min readread →
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