@developer.mozilla.org - MDN Web Docs

15 May 2026 03:00 +0000

🦊 New in Firefox 150: the revert-rule CSS keyword. Make a property behave as if the current rule didn't exist, letting a value from another matching rule take effect instead. Read Now 👇 https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/150

14 May 2026 04:00 +0000

🦊 Firefox 150: light-dark() now accepts image values — not just colors. Use it with images and gradients to adapt visuals based on color scheme. background: light-dark(url(light.png), url(dark.png)); Read Now 👇 https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/150

13 May 2026 06:00 +0000

🦊 Firefox 150 ships ariaNotify() on Document and Element. Queue text to be announced by a screen reader — a more ergonomic and reliable alternative to ARIA live regions. Read Now 👇 https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/150

12 May 2026 20:00 +0000

🦊 Firefox 150: color-mix() now accepts more than two colors at once. Mix any number of colors in a single declaration — no more nesting multiple calls. Read Now 👇 https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/150

12 May 2026 15:00 +0000

🦊 Firefox 150: is now supported. Lazy-loaded images use their calculated layout size to select from srcset — no more duplicating media queries in HTML. Read Now 👇 https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/150

11 May 2026 20:00 +0000

Have you heard of CSS Subgrid? 🤔 A grid item can now pass its parent's grid lines to children, so nested elements align perfectly with the outer layout. No more hacky workarounds for aligned nested grids. Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_grid_layout/Subgrid

11 May 2026 10:00 +0000

🆕 The URL Pattern API is Newly Available! Use it to match and extract parts of URLs, no need to reinvent routing logic. Supports literals, wildcards, named groups, and even regex constraints. Learn how it works 👇 https://developer.mozilla.org/en-US/docs/Web/API/URL_Pattern_API

11 May 2026 10:00 +0000

Firefox 150 ships 7 media pseudo-classes: :buffering, :muted, :paused, :playing, :seeking, :stalled, :volume-locked. Style and elements based on their playback state. Read Now 👇 https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/150

10 May 2026 16:00 +0000

Wait for all promises, even the failing ones 🔄 `Promise.allSettled()` waits for every promise to finish, success or failure. ⋅ Returns { status: 'fulfilled', value } or { status: 'rejected', reason } ⋅ Perfect for batch operations Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/allSettled

10 May 2026 10:00 +0000

✨ :only-child now matches elements with no parent! The :only-child selector has been updated — it can now match elements that have no parent at all, not just sole children. A subtle but useful spec alignment across all major browsers. Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/CSS/:only-child

09 May 2026 13:30 +0000

09 May 2026 07:29 +0000

Build smooth scroll experiences with CSS scroll snap 📜 Snap scrollable containers to specific positions — carousels, galleries, and paginated views with zero JavaScript. Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_scroll_snap https://developer.mozilla.org/en-US/docs/Web/CSS/Guides/Scroll_snap

08 May 2026 19:00 +0000

📬 Check own properties safely with Object.hasOwn() A safer alternative to hasOwnProperty, works even on objects with a null prototype. Baseline since 2022 ✅ Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/hasOwn

08 May 2026 15:01 +0000

Create frosted glass effects in CSS 🪟 backdrop-filter applies visual effects to the content behind an element - blur, brightness, contrast, and more. backdrop-filter: blur(10px) brightness(0.9); No JavaScript. No canvas tricks. Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/CSS/backdrop-filter

08 May 2026 03:00 +0000

The CSS next-sibling combinator (+) selects an element only when it immediately follows another, same parent, no elements between them. img + p { font-weight: bold; } Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Selectors/Next-sibling_combinator

07 May 2026 11:00 +0000

🆕 Document.caretPositionFromPoint() is Newly Available! Give it an (x, y) coordinate and get back the exact DOM node and character offset. Perfect for click-to-edit interfaces. Check it out 👇 https://developer.mozilla.org/en-US/docs/Web/API/Document/caretPositionFromPoint

07 May 2026 04:00 +0000

🆕 The Popover API is Baseline, no JavaScript needed Tooltips, dropdowns, and menus with just HTML attributes. ⋅ popover attribute on any element ⋅ popovertarget to wire the trigger ⋅ Accessible by default, no ARIA hacks Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/API/Popover_API

06 May 2026 12:00 +0000

Better error chaining is finally in JavaScript 🔗 `Error.cause` lets you attach the original error when rethrowing, keeping full context without losing the stack. Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause

06 May 2026 06:00 +0000

Speed up rendering with content-visibility: auto ⚡ This CSS property skips rendering off-screen content until needed, giving massive performance wins on long pages. ⋅ Pairs with contain-intrinsic-size ⋅ Zero-effort lazy rendering Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/CSS/content-visibility

05 May 2026 20:00 +0000

React to element size changes, not just the window 📐 `ResizeObserver` fires when any element's dimensions change, perfect for responsive components. ⋅ Observe padding box, content box, or border box ⋅ Works with dynamic DOM changes Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/API/ResizeObserver

05 May 2026 15:01 +0000

05 May 2026 11:57 +0000

Run non-critical work without blocking the UI 💤 `requestIdleCallback()` schedules tasks during browser idle time. ⚠️ Limited Availability ⋅ Runs only when the main thread is free ⋅ Great for analytics, prefetching, and cleanup Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/API/Window/requestIdleCallback

04 May 2026 10:00 +0000

JavaScript's date object has been tricky for years, but that is changing. The NEW Temporal API brings, 🌍 Easily handle time zones 📆 Precise date math 🕒 Parse ISO strings without errors ⌛ Durations, date ranges, and more. Start experimenting 👇 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Temporal

01 May 2026 15:00 +0000

JavaScript now has non-mutating array methods ✨ `toSorted()`, `toReversed()`, `toSpliced()`, and `with()` return new arrays instead of modifying the original. No more [...arr].sort() to avoid side effects. Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/toSorted

01 May 2026 03:00 +0000

30 Apr 2026 21:00 +0000

Show focus rings only when needed 🎯 :focus-visible applies styles when an element receives focus via keyboard, but not on mouse clicks. Better UX for everyone. Read More 👇 https://developer.mozilla.org/en-US/docs/Web/CSS/:focus-visible

30 Apr 2026 07:00 +0000

Transform streaming data on the fly 🔄 TransformStream sits between a readable and writable stream, letting you modify chunks as they pass through. Perfect for encoding, compression, or parsing. Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/API/TransformStream

29 Apr 2026 12:00 +0000

Did you know about Clear-Site-Data header? 👀 One HTTP header to clear cookies, storage, or cache for your site. Perfect for logout flows. Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Clear-Site-Data

29 Apr 2026 07:00 +0000

Schedule work at the right time with queueMicrotask() ⚡ Run a callback after the current task but before rendering. More predictable than setTimeout(fn, 0), lighter than a Promise. Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/API/Window/queueMicrotask

28 Apr 2026 21:00 +0000

Format lists like a native speaker 🌐 Intl.ListFormat turns arrays into grammatically correct strings in any locale. Handles "and", "or", and narrow styles automatically. Learn more 👇 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/ListFormat