Script async vs defer vs type=module: Loading Order Explained
When a plain script blocks parsing, why async runs in arrival order and defer in document order, and how module scripts fit, tested in Chrome.
~7 min readread →
Developer interview notes & guides — Page 1
Focused explanations and longer guides, with worked scenarios, common mistakes and interview exercises across every chapter.
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Showing 1–24 of 200 articles
call vs apply vs bind in JavaScript: Differences With Examples
call and apply run a function now with a chosen this; bind returns a new function for later. Covers arguments, borrowing and the listener trap.
~6 min readread →
Callbacks vs Promises vs Async/Await in JavaScript Explained
One task written three ways (callbacks, promise chains, async/await) with error handling, parallel work and the return-await trap, run in Node.
~6 min readread →
localStorage vs sessionStorage vs Cookies: Key Differences
How long each lasts, who can read it, what goes to the server, and why HttpOnly cookies beat localStorage for session tokens when XSS is in play.
~7 min readread →
map vs forEach vs for...of in JavaScript: Which Loop to Use
map builds a new array, forEach runs side effects and returns undefined, for...of can break. See sparse arrays, chaining and the parseInt trap.
~6 min readread →
INNER JOIN vs LEFT JOIN: Differences and the WHERE Trap
INNER JOIN keeps only matching rows; LEFT JOIN keeps every left row and fills gaps with NULL. See counts, anti-joins and the WHERE filter trap.
~6 min readread →
UNION vs UNION ALL in SQL: Duplicates and Performance
UNION removes duplicate rows after combining two queries; UNION ALL keeps every row and skips the sort or hash. Learn when each is correct.
~6 min readread →
Angular Global Error Handling
What actually reaches Angular's ErrorHandler, how to write one that never throws or loops, and where HTTP and chunk-load errors belong.
~6 min readread →
Angular Resource API for Async Data
How resource() turns a signal-driven request into value, status and error signals, cancels stale loads, and why value() can throw on error.
~6 min readread →
Angular Zoneless Change Detection
Without zone.js, Angular renders only when notified. See which updates notify, which silently don't, and how TestBed catches the gaps for you.
~6 min readread →
JavaScript Array Methods: Mutating Versus Returning New
Which JavaScript array methods change the array in place, which return a new one, and how toSorted, toSpliced and with fix the old traps.
~6 min readread →
JavaScript Date and Timezone Pitfalls
Why new Date('2026-03-08') can show March 7, how DST breaks adding 24 hours, and how to store, compute and display dates in JavaScript safely.
~7 min readread →
JavaScript Optional Chaining and Nullish Coalescing
How ?. short-circuits a whole chain, how ?? differs from ||, and when optional chaining hides a real bug instead of handling missing data.
~6 min readread →
Node.js URL and URLSearchParams
Build query strings with URLSearchParams, resolve relative URLs against a base, and check protocol and host before your server fetches.
~7 min readread →
React Live Regions and Screen Reader Announcements
Announce cart updates, result counts and errors to screen readers from React: why live regions must already exist, and how to repeat a message.
~6 min readread →
React Context Splitting for Performance
Why every React context consumer re-renders when any part of the value changes, and how splitting state, actions and slow-changing data fixes it.
~6 min readread →
React lazy Loading and Code Splitting
Split React bundles with lazy and Suspense, preload chunks before the click, and handle the chunk-load failures that follow every deploy.
~7 min readread →
React Portals and Event Bubbling
Events from a React portal bubble through the React tree, not the DOM. Here is what that breaks in click-outside logic, and how to fix it.
~6 min readread →
React StrictMode and Double-Invoked Effects
What StrictMode calls twice in development, the exact mount, unmount, mount sequence in React 19, and how to fix the effects it exposes.
~6 min readread →
React useOptimistic and Instant Feedback
Show a sent message before the server answers with useOptimistic, see how it rolls back on failure, and avoid the outside-transition trap.
~6 min readread →
React Imperative Handles with useImperativeHandle
Expose a small focus() and clear() API from a React component with useImperativeHandle, pass refs as props in React 19, and know when not to.
~6 min readread →
PostgreSQL CASE Expressions
How CASE evaluates branches in order, why a missing ELSE or WHEN NULL quietly returns NULL, and how to pivot counts with conditional aggregates.
~7 min readread →
PostgreSQL Self-Joins
Join a table to itself to show each employee's manager, pair rows without mirror duplicates and find repeated emails before cleanup.
~6 min readread →
PostgreSQL Set Operations
Combine queries with UNION, INTERSECT and EXCEPT, predict their duplicate and NULL handling, and see where EXCEPT beats NOT IN.
~6 min readread →
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