JavaScript Fundamentals
More to discover ↗Keep component CSS predictable by using a root class for ownership, classes for variants, and custom properties for values that should change. This guide builds a reusable notice component and explains how to avoid accidental styling across a page.
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Interface Components
More to discover
Reusable components are easier to build and maintain when each one has a clear job and owns a defined part of the DOM. Learn how to separate configuration from state, handle events within a component boundary, and clean up when a component is removed.
Read article · 4 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↗A practical workflow for checking focus order, visible focus, labels, structure, and dynamic updates. Use a small sample page to compare what a keyboard user can do with what a screen reader user can understand.
Read article · 4 min↗An icon can suggest what a control does, but it may not tell every user its purpose. Learn how to name icon-only buttons, when tooltips help, and how to check the result with a keyboard and accessibility inspector.
Read article · 4 min↗A page can be visually readable yet sound wrong when a screen reader encounters text in another language. Learn how to set a document’s language, mark changes within a page, and test pronunciation without confusing language with text direction.
Read article · 4 min↗A practical guide to making data tables easier to understand and navigate. Learn when to use a caption, how to associate header cells with data cells, and what to check when a table becomes more complex.
Read article · 4 min↗A page can change without moving keyboard focus or reloading. Learn when ARIA live regions help, how to announce updates without overwhelming people, and how to test the result in a simple browser example.
Read article · 4 min↗Motion can help explain an interface, but it can also distract or cause discomfort. Learn how to use CSS and browser APIs to respect reduced-motion preferences without hiding content or losing important feedback.
Read article · 4 min↗Captions, transcripts, and audio descriptions serve different purposes. Learn how to choose the right combination for videos, podcasts, and other web media, then check that people can find and use it.
Read article · 4 min↗A page can look responsive at a narrow viewport yet break when someone enlarges its text. Learn how to build flexible layouts, protect component content, and test zoom and text resizing in a reproducible browser setup.
Read article · 4 min↗A green banner or red border may look clear, but color should not carry a status message by itself. Learn how to pair color with readable text, useful placement, and appropriate screen-reader announcements.
Read article · 4 min↗Learn what to compare when checking contrast in a web interface, how text and control requirements differ, and how to test real component states rather than isolated color swatches.
Read article · 4 min↗A skip link lets keyboard users move past a repeated header or navigation menu and reach the main content. Learn where to place one, how to make it visible on focus, and how to check that it works.
Read article · 4 min↗Use a link when someone is going somewhere and a button when they are doing something. Learn how that distinction affects keyboard behavior, forms, client-side routing, disabled states, and accessible testing.
Read article · 4 min↗A modal dialog should bring keyboard focus into the dialog, keep the rest of the page unavailable while it is open, and return focus to a sensible place when it closes. Learn a practical approach using the native HTML dialog element and a small amount of JavaScript.
Read article · 4 min↗Keyboard navigation is easier to build when you start with the document’s natural order, keep focus visible, and test what happens when an interface changes. Learn a repeatable way to check links, forms, menus, and dialogs without making assumptions about how people navigate.
Read article · 4 min↗A practical approach to form validation that makes errors discoverable, connects each message to its field, and lets people correct mistakes without starting over.
Read article · 4 min↗A form is easier to use when each input has a clear name, nearby instructions, and useful feedback. Learn how to label fields, explain formats, group related choices, and connect errors to the inputs they describe.
Read article · 4 min↗An image does not need a spoken description simply because it appears on a page. Learn how to decide whether an image is decorative, give decorative HTML images empty alternative text, and check that meaningful content remains available to everyone.
Read article · 3 min↗Alternative text helps people understand an image when they cannot see it. Learn how to identify an image’s purpose, write concise descriptions that fit the surrounding content, and check your choices in a web interface.
Read article · 4 min↗A clear page outline helps people scan content, move between sections, and find the main task. Learn how to combine descriptive headings with HTML landmarks, then check the result using keyboard navigation and accessibility tools.
Read article · 4 min↗Semantic HTML gives a page a structure that browsers and assistive technologies can interpret. Learn how to choose landmarks, headings, lists, links, buttons, and form controls by the job they do, then check whether the resulting page makes sense without its visual styling.
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