Page 10 - JavaScript

An error inside an async function disappears without a trace, the console shows an unhandled rejection, an empty catch block hides exactly the problem you were looking for. Promise error handling follows its own rules, different from synchronous try catch. This article shows the concrete pitfalls and how to reliably avoid them.

The MutationObserver is the modern, efficient alternative to DOMSubtreeModified and polling-based approaches to watching the DOM. It reacts asynchronously to attribute, child-node and text changes in the DOM, without the rendering-thread blocking that the old mutation events caused.

The Storage Manager API answers two questions that every offline application eventually faces: how much storage space is actually available to the origin, and how do you prevent the browser from simply deleting that data under storage pressure. Anyone who correctly uses quota calculation and persistence requests builds applications that avoid data loss proactively instead of explaining it after the fact.

Server side rendering delivers visible content quickly, but hydration often makes that content interactive only after a delay. Lazy hydration shifts exactly that delay to where nobody notices it: to components that are not yet visible or are not currently needed.

The Origin Private File System is an isolated, high performance file store per origin that reaches direct file system speed through synchronous read and write handles inside web workers. It powers Wasm databases, image editors and offline tools that clearly outperform classic IndexedDB based solutions in throughput and latency.

Tree shaking is the process by which modern bundlers remove unused JavaScript code from the final bundle. What sounds simple has complex prerequisites: ES modules are mandatory, certain code patterns block tree shaking, and misconfigured sideEffects flags can eliminate or preserve entire modules, with measurable effects on load times.

After years of wrangling in the TC39 committee, JavaScript decorators have reached Stage 3. They enable class-level metaprogramming without Babel hacks: logging, memoization, validation and dependency injection as reusable annotations.

Promise.allSettled waits for every given promise, regardless of whether individual ones fulfill or reject, and delivers its own status per result. For batch requests where a single failure should not wreck the entire operation, that is the right foundation instead of the fail-fast behavior of Promise.all.

A recording in the Performance Panel looks at first glance like a colorful bar chart. Combining Flame Chart, Call Tree, Bottom Up and Event Log reveals the actual cause of jank, a blocked main thread and poor Web Vitals, instead of just treating symptoms.

ESM and CommonJS are two fundamentally different module systems that must coexist in the same Node runtime, and that is exactly where ESM/CJS interop problems come from. Anyone who does not understand the difference between require() and import will eventually hit ERR_REQUIRE_ESM, lost named exports, or a broken instanceof check caused by a dependency loaded twice.