Topic
157 posts tagged “JavaScript”.
Takina · · 4 min read Object.groupBy() buckets array items by a key you compute, replacing the reduce() boilerplate developers have written for years. How it works.
Takina · · 4 min read Structural typing checks shape, not name — TypeScript treats two differently-named types as compatible if their members match, unlike nominal systems.
Takina · · 3 min read Import attributes let JavaScript modules declare a resource's expected type at import time, such as JSON — catching mismatches before code runs.
Takina · · 4 min read The Streams API lets JavaScript process data as chunks arrive instead of buffering it all in memory. How ReadableStream, WritableStream, and pipes work.
Takina · · 4 min read Workspaces let npm and pnpm manage multiple packages in one repository, sharing a single dependency tree and letting packages reference each other locally.
Takina · · 4 min read The Web Locks API lets JavaScript acquire named locks shared across tabs, so only one tab does work like a token refresh or a write at a time.
Chisato · · 4 min read The Trusted Types API blocks DOM-based XSS by forcing risky DOM sinks like innerHTML to accept only vetted objects instead of raw strings.
Takina · · 4 min read Biome is a Rust-based linter and formatter that replaces ESLint and Prettier with one faster tool, one config file, and no plugin ecosystem to manage.
Takina · · 4 min read Svelte 5 runes like $state and $derived replace the old reactive-assignment magic with explicit function calls that work anywhere in a file.
Takina · · 5 min read Variance decides when TypeScript accepts Array<Dog> where Array<Animal> is expected — covariant, contravariant, or invariant, explained with examples.
Takina · · 4 min read A shallow copy duplicates an object's top-level properties but shares nested references; a deep copy duplicates everything recursively. How to do each.
Takina · · 4 min read Canvas draws immediate-mode pixels you redraw yourself; SVG keeps a live, styleable DOM of vector shapes. Here's how to pick between the two.
Takina · · 5 min read toSorted(), toReversed(), toSpliced(), and with() copy an array instead of mutating it, fixing a long-standing footgun in JavaScript's Array API.
Takina · · 3 min read A SharedWorker runs one script shared across every tab and window of the same origin — a single background thread they can all connect to and message.
Takina · · 5 min read Zod infers static TypeScript types directly from its schemas; Yup was built for JavaScript form validation first. How the two approaches differ.
Takina · · 4 min read Bun and Deno both aim to replace Node.js with a faster, more batteries-included runtime. How their runtimes, tooling, and compatibility differ.
Takina · · 5 min read A .d.ts file describes a library's types without its implementation. How TypeScript declaration files work, and how to write one for an untyped JS package.
Takina · · 4 min read A TypeScript tuple is a fixed-length array where each position has its own type. How tuples work, labeled elements, and when to use them over arrays.
Takina · · 5 min read ResizeObserver watches an element's size; IntersectionObserver watches its visibility. Both replace scroll/resize listeners — here's when to use each.
Takina · · 4 min read Most regex engines backtrack through an NFA; a few compile to a DFA instead. The difference explains why some patterns hang forever and others never do.
Takina · · 4 min read JavaScript private class fields use a # prefix to enforce true encapsulation at the language level, hiding state that closures and underscores never could.
Takina · · 4 min read An index signature lets a TypeScript type describe objects whose keys aren't known in advance. How the syntax works, and when to reach for a Record instead.
Takina · · 4 min read JavaScript's iterator helper methods bring map, filter, and take directly to iterators, so lazy sequences no longer need a library or a manual loop.
Takina · · 4 min read JavaScript's Reflect object mirrors fundamental object operations as functions, designed to pair with Proxy traps and simplify metaprogramming.
The Lycoris Team · · 4 min read TypeScript's moduleResolution setting decides how import paths map to files. How node10, node16, and bundler resolution differ, and which to pick.
Takina · · 4 min read The Navigation API gives JavaScript a structured way to intercept and control browser navigations — a modern alternative to the History API.
Takina · · 3 min read Array.sort() converts elements to strings by default, so numbers sort out of order. Here's why, and how a compare function fixes it.
Takina · · 5 min read The BroadcastChannel API lets same-origin tabs, windows, and workers pass messages to each other instantly, with no server round trip or polling.
Takina · · 4 min read useMemo caches a computed value; useCallback caches a function reference. Both skip work on re-render, but they memoize different things.
Takina · · 4 min read React's Context API passes data through the component tree without manually threading props at every level — and where it stops being the right tool.
Takina · · 4 min read setTimeout runs a callback once after a delay; setInterval repeats it on a fixed cadence — but drifts under load in ways setTimeout recursion avoids.
Takina · · 4 min read TypeScript is JavaScript plus a compile-time type system — same runtime, different guarantees. Where each one wins and how they fit together.
Takina · · 3 min read JavaScript's Set object now has built-in union, intersection, difference, and subset methods — replacing manual loops for combining collections.
Takina · · 5 min read Top-level await lets a JavaScript module pause at import time without wrapping code in an async function. How it works and when it bites.
Takina · · 5 min read Hydration re-runs a framework's JS to attach interactivity after render; resumability serializes state so the browser can skip that work.
Takina · · 4 min read Node's cluster module forks whole processes to use every CPU core; worker_threads share memory inside one process. How to pick between them.
Takina · · 5 min read Nx and Turborepo both speed up monorepo builds with caching and task graphs — the real difference is scope, plugins, and how much structure you want.
Takina · · 4 min read Strict mode turns silent JavaScript mistakes into thrown errors and closes off unsafe legacy behavior. Modules and classes use it by default.
Takina · · 4 min read BigInt is JavaScript's built-in type for whole numbers beyond Number's safe limit. How the syntax works, what it can't do, and when you actually need it.
Takina · · 4 min read esbuild, Rollup, and webpack all bundle JavaScript, but trade off speed, configurability, and output shape differently. Which fits which project.
Takina · · 4 min read JavaScript frees memory automatically by tracking reachability, not reference counts. How the mark-and-sweep algorithm works and what causes leaks anyway.
Takina · · 4 min read requestAnimationFrame schedules work right before the next repaint; requestIdleCallback runs only when the browser is otherwise idle. When to use each one.
Takina · · 4 min read Node's Buffer class holds raw binary data outside the V8 heap, letting Node handle files, sockets, and streams efficiently. Here's how it works.
Takina · · 4 min read ArrayBuffer allocates raw binary memory; typed arrays like Uint8Array give it a numeric type and view. How JavaScript handles binary data directly.
Takina · · 4 min read Deno vs Node.js compared: security model, TypeScript support, module resolution, and when each runtime is the better choice.
Takina · · 5 min read Hoisting moves variable and function declarations to the top of their scope before code runs, which explains some of JavaScript's most confusing bugs.
Takina · · 4 min read Node.js worker threads run JavaScript on real OS threads in parallel, letting CPU-heavy work run without blocking the event loop.
Takina · · 4 min read The URL API parses, builds, and validates URLs natively in JavaScript — no regex needed. How URL and URLSearchParams work, with practical examples.
Takina · · 4 min read The Clipboard API lets web pages read and write the system clipboard asynchronously, replacing the old execCommand copy/paste hacks with a real API.
Takina · · 4 min read The Web Share API lets a web page open the device's native share sheet to send text, links, or files to other apps, no clipboard hack required.
Takina · · 5 min read Virtual scrolling renders only the rows visible in the viewport, keeping the DOM small so lists with tens of thousands of items stay smooth.
Takina · · 4 min read Remix and Next.js both extend React with routing and data loading, but differ sharply in rendering model, data fetching, and deployment targets.
The Lycoris Team · · 4 min read Vitest and Jest share a similar API, but Vitest's Vite-based architecture makes it faster with native ESM. How the two test runners compare.
Takina · · 3 min read The Web Animations API lets JavaScript create and control animations natively, combining CSS-animation performance with imperative, scriptable control.
Takina · · 4 min read The MutationObserver API watches for changes to the DOM — attributes, child nodes, and text — without polling. How it works and when to use it.
Takina · · 3 min read SharedArrayBuffer lets JS threads share raw memory; Atomics provides race-free operations on it. How true multi-threaded data sharing works in JS.
Takina · · 4 min read A polyfill is code that implements a missing browser feature so older environments behave as if they supported it natively.
The Lycoris Team · · 4 min read Tail call optimization reuses a function's stack frame for its final call instead of pushing a new one, turning some recursion into constant stack space.
Takina · · 5 min read Branded types attach a compile-time-only tag to a primitive so TypeScript rejects mixing values that share a shape but not a meaning.
Takina · · 4 min read flat() flattens nested arrays by a given depth; flatMap() maps then flattens one level in a single pass. How each works and when to pick one.
Takina · · 4 min read The History API lets JavaScript change the URL and manage browser history without a page reload, which is what makes client-side routing possible.
Takina · · 4 min read Zustand is a minimal hook-based store with almost no boilerplate; Redux is a stricter, more structured pattern built for large, predictable state trees.
Takina · · 4 min read Declaration merging lets TypeScript combine multiple declarations of the same name into one — the mechanism behind extending interfaces and global types.
Takina · · 4 min read The App Router uses React Server Components and nested layouts; the Pages Router is Next.js's original file-based model. How they differ and when to pick each.
Takina · · 4 min read Object.freeze() locks an object completely; Object.seal() only stops adding or removing properties. How the two immutability methods differ.
Takina · · 4 min read Abstract classes in TypeScript define shared implementation plus methods subclasses must fill in. How they differ from interfaces and when to reach for them.
Takina · · 3 min read React Suspense lets components pause rendering while they wait on async data, showing a fallback UI instead of manual loading-state juggling.
Takina · · 4 min read The Page Visibility API tells JavaScript when a tab is hidden or visible, so you can pause polling, animations, and timers the user can't see.
Takina · · 4 min read A lockfile records the exact dependency versions your package manager resolved, so every install — from your laptop to CI — reproduces the same tree.
Takina · · 3 min read never represents values that can't exist — it marks unreachable code, exhaustive switches, and functions that always throw or loop forever.
Takina · · 4 min read TypeScript's readonly keyword blocks reassignment at compile time for properties, arrays, and tuples — with no runtime enforcement at all.
Takina · · 4 min read The Intl API formats dates, numbers, and currency using a user's locale without a library. How Intl.DateTimeFormat and Intl.NumberFormat work.
Takina · · 4 min read requestIdleCallback runs low-priority JavaScript when the browser is idle, without blocking rendering, input, or the main thread.
Takina · · 5 min read Turbopack is a Rust-based bundler built for incremental speed; Webpack is the mature, plugin-heavy standard. How they differ and when to pick each.
Takina · · 5 min read Promise.all() fails fast, allSettled() waits for every result, and race() returns whichever promise finishes first — how to choose correctly.
Takina · · 4 min read JavaScript's dynamic import() loads a module on demand and returns a promise, letting you split bundles and defer code until it's actually needed.
Takina · · 4 min read The spread operator (...) expands an iterable into individual elements; the rest operator collects elements back into an array. Same syntax, opposite jobs.
Takina · · 4 min read TypeScript's as const assertion locks a value to its literal, readonly type instead of widening it. How it works and when to reach for it.
Takina · · 4 min read The ResizeObserver API lets JavaScript watch an element's box size and react without polling or resize-event hacks. How it works and when to use it.
Takina · · 5 min read A JavaScript memory leak happens when a reference outlives its usefulness and the garbage collector can't reclaim it. Common causes and how to find them.
Takina · · 4 min read localStorage, sessionStorage, and cookies all store data in the browser, but differ in lifetime, size limits, and whether the server can see them.
Takina · · 4 min read Import maps let browsers resolve bare module specifiers like "react" to real URLs, enabling native ES module imports without a bundler.
Takina · · 5 min read The Push API lets a web app send notifications through a service worker, even when the site isn't open in a browser tab. Here's the full flow.
Takina · · 5 min read JavaScript destructuring unpacks values from arrays and objects into variables in one expression. How it works, with the rest and spread operators.
Takina · · 4 min read How JavaScript determines what this refers to: default, implicit, explicit, and new binding, plus why arrow functions behave differently.
The Lycoris Team · · 4 min read A monad is a wrapper type with rules for chaining operations that might fail, be async, or carry extra context — like Promise or Optional, generalized.
Takina · · 5 min read Type guards are functions and checks that narrow a TypeScript union to a specific type at runtime. How typeof, instanceof, in, and custom guards work.
Takina · · 4 min read TypeScript function overloads let one function name accept multiple call signatures with different types. How overload signatures work and when to use them.
Takina · · 4 min read Tagged template literals let a function intercept a template string's parts before interpolation — the mechanism behind safe SQL, styled-components, and i18n.
Takina · · 5 min read IndexedDB is a browser API for storing large amounts of structured data client-side, with indexes, transactions, and no size limit like localStorage.
Takina · · 4 min read Event delegation attaches one listener to a parent instead of one per child, using event bubbling to catch clicks from elements added after page load.
Takina · · 4 min read The Intersection Observer API tells you when an element enters or leaves the viewport, without scroll-event polling. How it works and where to use it.
Takina · · 4 min read structuredClone() is a built-in JavaScript function for deep-copying values, including cycles and typed arrays, without the workarounds JSON tricks require.
Takina · · 4 min read tsconfig.json controls how TypeScript checks and compiles your code. Here are the options that actually change behavior, and the ones you can leave alone.
Takina · · 4 min read Template literal types let TypeScript build string types from other types, like JavaScript template strings. How they work, with practical patterns.
Takina · · 4 min read The Fetch API is JavaScript's built-in interface for making HTTP requests. How it works, its promise-based flow, and where it trips people up.
Takina · · 4 min read TypeScript's interface and type both describe object shapes, but they diverge on declaration merging, unions, and extension. When to reach for each.
Takina · · 4 min read requestAnimationFrame schedules a callback right before the browser repaints, syncing JavaScript animation to the display's refresh rate. How it works.
Takina · · 4 min read Solid.js uses fine-grained signals and no virtual DOM; React re-renders components and diffs. How the two reactivity models differ in practice.
Takina · · 5 min read SSE streams one-way updates over plain HTTP; WebSockets open a full-duplex channel. How they differ and which fits your real-time feature.
Takina · · 4 min read Mapped types transform one type into another by iterating over its keys — the mechanism behind Partial, Readonly, Record, and Pick under the hood.
Takina · · 4 min read TypeScript enums group named constants under one type. How numeric, string, and const enums compile, and when a union type is the better choice.
Takina · · 4 min read A JavaScript Symbol is a guaranteed-unique primitive used for collision-free object keys. How Symbols work, well-known Symbols, and when to use them.
Takina · · 4 min read A discriminated union tags each variant of a type with a shared literal field, letting TypeScript narrow the type automatically inside a switch or if check.
Takina · · 4 min read var, let, and const differ in scope, hoisting behavior, and reassignment rules. Here's what each one actually does and when to reach for it.
Takina · · 4 min read ESLint catches bugs and enforces code patterns; Prettier only reformats how code looks. Why most JavaScript projects run both, not one or the other.
Takina · · 4 min read Optional chaining (?.) short-circuits on null or undefined instead of throwing; nullish coalescing (??) supplies a default only for null or undefined.
Takina · · 4 min read Prototypal inheritance means JavaScript objects inherit properties directly from other objects via a prototype chain, not from classes. How it works.
Takina · · 4 min read Web workers run scripts off the main thread for parallel computation. Service workers intercept network requests for offline and caching. How they differ.
Takina · · 4 min read map, filter, and reduce transform arrays without loops or mutation. How each one works, when to reach for it, and where they trip people up.
Takina · · 4 min read TypeScript's unknown forces a type check before use; any opts out of type checking entirely. When to reach for each in real code.
Takina · · 4 min read A source map is a file that maps minified, bundled, or transpiled code back to its original source, so debuggers and stack traces stay readable.
Takina · · 4 min read Conditional types let TypeScript pick a type based on another type, using T extends U ? X : Y — the foundation of most advanced type utilities.
Takina · · 3 min read Currying transforms a multi-argument function into a chain of single-argument functions. How currying and partial application work in JavaScript.
Takina · · 4 min read Vue uses a template syntax with a reactive proxy system; React uses JSX with a virtual DOM. How the two frameworks differ and when to pick each.
Takina · · 4 min read Node.js streams process data in chunks instead of loading it all into memory. How readable, writable, and transform streams work, and when to reach for them.
Takina · · 5 min read A WeakMap holds object keys without blocking garbage collection, unlike a regular Map. How WeakMap and WeakRef work and when to reach for them.
Takina · · 4 min read JavaScript's Map and Set are built-in collections with cleaner semantics than plain objects and arrays. Here's how each works and when to reach for one.
Takina · · 4 min read The Temporal API is JavaScript's built-in replacement for Date — immutable, timezone-aware objects for dates, times, and durations.
Takina · · 4 min read TypeScript's satisfies operator checks a value against a type without widening or erasing its inferred literal type. Here's when to reach for it.
Takina · · 4 min read TypeScript decorators attach reusable behavior to classes and members with an @ syntax. How class, method, and field decorators work, with real examples.
Takina · · 4 min read Shadow DOM attaches an isolated DOM tree to an element so a component's styles and markup can't leak in or out. Here's how it actually works.
Takina · · 4 min read npm, pnpm, and Yarn all install the same packages but differ in speed, disk usage, and monorepo support. Here's how to pick the right one.
Takina · · 4 min read AbortController lets JavaScript cancel an in-flight fetch or async task on demand, preventing stale responses from overwriting newer state.
Takina · · 5 min read ESM and CommonJS are JavaScript's two module systems — how import/export differs from require/module.exports, and when each one is used.
Chisato · · 3 min read Cross-site scripting (XSS) injects malicious scripts into pages other users view. How stored, reflected, and DOM-based XSS work, and how to prevent them.
Takina · · 4 min read Optimistic UI updates the interface immediately, before the server confirms a change, then rolls back if the request fails — for apps that feel instant.
Takina · · 4 min read Web Components are browser-native APIs for building reusable, encapsulated custom elements that work in any framework, or none at all.
Takina · · 4 min read TypeScript utility types like Partial, Pick, Omit, and Record transform existing types instead of redeclaring them. How the common ones work, with examples.
Takina · · 4 min read A monorepo holds multiple projects in one repository with shared tooling and atomic commits. How it compares to splitting projects across separate repos.
Takina · · 4 min read Generators are functions that pause and resume with the yield keyword, producing values lazily on demand instead of computing them all at once.
The Lycoris Team · · 4 min read Memoization caches a function's return value by its input, skipping recomputation on repeat calls. How it works and when it actually helps.
Takina · · 4 min read TypeScript generics let functions and types work with any type while preserving the specific type used at each call site, avoiding both duplication and any.
Takina · · 4 min read Async/await is syntactic sugar over Promises, not a different mechanism. How each looks in practice, and when to still reach for raw Promises.
Takina · · 4 min read The virtual DOM is an in-memory copy of the UI tree that frameworks diff against the previous version to batch and minimize real DOM updates.
Chisato · · 4 min read A Content Security Policy is an HTTP header that restricts what scripts and resources a page can load, blocking most XSS attacks by default.
Takina · · 4 min read A JavaScript Proxy wraps an object and intercepts operations like get and set through traps. How traps work, with practical examples and Reflect.
Takina · · 4 min read A web worker runs JavaScript on a background thread, freeing the main thread to keep the UI responsive. How workers communicate and when to use one.
Takina · · 5 min read Svelte compiles away at build time; React ships a runtime and virtual DOM. Bundle size, reactivity model, and ecosystem tradeoffs compared.
Takina · · 5 min read Microsoft shipped TypeScript 7.0 with a Go-native compiler that's roughly 10x faster than 6.0. What changed, what breaks, and how to upgrade.
Takina · · 4 min read Tree shaking removes unused exports from a JavaScript bundle at build time, shrinking file size by relying on ES module static structure.
Takina · · 5 min read A JavaScript closure is a function that remembers the variables from where it was defined. How closures work, why they matter, and the classic loop gotcha.
Takina · · 5 min read Debounce and throttle both tame rapid-fire events, but differently — debounce waits for a pause, throttle enforces a steady rate. When to use each.
Takina · · 3 min read htmx lets you build dynamic, interactive pages with HTML attributes — no SPA, no build step. Learn the core ideas and ship a working live-search example in minutes.
Takina · · 4 min read WebRTC lets browsers stream audio, video, and data directly between peers — no plugins. How getUserMedia, RTCPeerConnection, and ICE/STUN/TURN fit together.
Takina · · 5 min read Static sites don't need a search server. Learn how Pagefind indexes your HTML at build time and adds fast, client-side full-text search for free.
Takina · · 4 min read A WebSocket is a protocol for full-duplex, persistent communication over a single TCP connection. Learn how it works, when to use it, and what the alternatives are.
Takina · · 4 min read CORS lets a server opt in to cross-origin browser requests, relaxing the same-origin policy in a controlled way. Why it exists and how to fix CORS errors.
Takina · · 4 min read JavaScript is single-threaded, yet pages stay responsive. A clear tour of the call stack, task queue, and microtasks — with examples you can run.
Takina · · 5 min read Signals offer fine-grained reactivity with automatic dependency tracking — and nearly every major framework has adopted them. Here's why the model won.
Takina · · 4 min read The View Transitions API brings smooth, app-like transitions to the web without a heavy SPA framework. Here's how it works and how to use it today.
Takina · · 5 min read An honest comparison of Bun and Node.js in 2026 — speed, ecosystem, built-in tooling, and when each runtime actually wins.
Takina · · 3 min read JavaScript is the programming language that makes web pages interactive. Learn how it works alongside HTML and CSS, and why it runs nearly everywhere.
Takina · · 5 min read React Server Components render exclusively on the server and stream a serialized result — no client JS shipped for that component. Here's what that actually means.
Takina · · 4 min read The DOM is the live in-memory tree browsers build from your HTML, which JavaScript reads and manipulates. Learn how it works and why it matters.
Takina · · 3 min read TypeScript adds a safety net to JavaScript without slowing you down. Here's how to set it up, the handful of concepts that matter, and how to adopt it gradually.
Takina · · 4 min read Server-Sent Events stream real-time updates over a single HTTP connection. How SSE works, when to use it, and how it compares to WebSockets.
