JavaScript Fundamentals
More to discover ↗The browser can report a change in network connectivity, but it cannot promise that your server is reachable. Learn how to use online and offline events for a helpful status message while handling request failures separately.
Read article · 3 min↗An AbortController can remove a group of DOM event listeners when a widget is finished. Try a small browser-console example, then learn where this cleanup pattern helps and what it does not clean up.
Read article · 3 min↗Learn how to request a one-time location after a user action, distinguish permission denial from other geolocation errors, and design a useful fallback when location is unavailable.
Read article · 4 min↗A hidden tab may still have JavaScript work scheduled. Learn how to use the Page Visibility API to pause optional work, resume it without duplicate timers, and handle the limits of visibility events.
Read article · 3 min↗A Web Worker can keep an interface responsive while JavaScript performs a substantial calculation. Learn how to send work to a worker, return a result, and handle practical limits such as message overhead and cancellation.
Read article · 4 min↗A browser can read a file that a visitor chooses without sending it to a server. Learn how to select a text file, read it with the File API, display it safely, and account for file size and reading errors.
Read article · 3 min↗Learn how to use the browser Clipboard API for copy and paste controls, when permission or user interaction may be required, and how to keep the interface useful when clipboard access fails.
Read article · 4 min↗Learn what browser timers do, why their delays are not exact, and how to cancel or reschedule work safely. Includes small examples you can try in a browser console.
Read article · 4 min↗Learn how to schedule visual updates with requestAnimationFrame, use its timestamp for consistent motion, and stop a loop cleanly. A self-contained browser-console example demonstrates the pattern.
Read article · 4 min↗MutationObserver lets browser code respond when elements, attributes, or text nodes change. Learn what it observes, how to set it up, and how to keep the callback focused.
Read article · 4 min↗ResizeObserver lets a JavaScript interface respond when an element changes size, even if the browser window stays the same. Learn when to use it, how to observe a panel, and how to avoid layout feedback loops.
Read article · 4 min↗Learn how to use IntersectionObserver to detect when page elements enter the viewport, understand its options, and clean up observers when they are no longer needed.
Read article · 4 min↗Learn when to use pushState and replaceState, how to render a view after Back or Forward navigation, and what the History API does not do for you.
Read article · 4 min↗Learn how to read, change, and remove query parameters in the browser using URL and URLSearchParams. Includes reproducible examples, guidance for repeated keys, and a practical way to update the address bar without reloading the page.
Read article · 4 min↗Learn when IndexedDB is useful, how databases and object stores fit together, and how to save and retrieve a JavaScript object with a reproducible browser example.
Read article · 4 min↗localStorage and sessionStorage share a simple API, but they differ in lifetime and how data is shared between tabs. Learn when each fits, why either can be unavailable, and how to provide a predictable fallback.
Read article · 4 min↗A practical guide to the browser’s cross-origin request rules. Learn how origins are defined, why a request can reach a server but still fail in JavaScript, when preflight happens, and which response headers a server needs to send.
Read article · 4 min↗A successful fetch call does not necessarily mean a successful HTTP response. Learn how to check response.ok, distinguish request failures from invalid JSON, and test each case in a browser.
Read article · 4 min↗A practical guide to the path a browser event takes through the DOM, with console examples that distinguish propagation from default browser behavior.
Read article · 4 min↗A click listener attached directly to a button cannot handle a different button created later. Learn how to listen on a stable parent, identify the intended target, and keep dynamic interfaces manageable.
Read article · 3 min↗DOMContentLoaded and load mark different milestones in a browser page’s startup. Learn which event to use for DOM setup, when to wait for images and other resources, and how script placement and document.readyState affect reliable initialization.
Read article · 4 min↗Learn how to find an element with querySelector, change its text with textContent, and represent interface state with classList. A small browser-console example shows how the three APIs work together.
Read article · 4 min↗
