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MDN is 20 years old! 🥳 🙏 A huge thank you to... The devs who read and trust MDN The contributors who improve it Everyone working on the web platform who shares our mission. Here's how we celebrated with the web.dev team! 🧁 developer.mozilla.org/en-US/blog/mdn…

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 👇 developer.mozilla.org/en-US/docs/Web…

@apidcloud Yes, it's Newly Available. 🫡

@MozDevNet Too bad it’s only supported starting iOS 26 😩

🆕 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 👇 developer.mozilla.org/en-US/docs/Web…

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 👇 developer.mozilla.org/en-US/docs/Web…

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 👇 developer.mozilla.org/en-US/docs/Web…

@jantimon Good catch! Clear-Site-Data: "cache" is often used on logout to prevent sensitive data from sticking around, but without consistent BFCache eviction, hitting “back” could still restore a full page snapshot.

@MozDevNet only recently in 2025 FireFox added full support for Clear-Site-Data (Bug 1930501) finally all browsers will remove the back-forward-cache on Clear-Site-Data: "cache" before that browser back after logout would show you private information from cache

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 👇 developer.mozilla.org/en-US/docs/Web…

@ArmEagle We occasionally reshare posts to extend their reach. With algorithm-driven feeds, not all followers see content the first time it’s published. 😄

@MozDevNet Yes. Because you wrote about that 19 days ago already: x.com/MozDevNet/stat…

@scriptquiz Link please! 🙌

@MozDevNet Love this so much. I did an entire talk on this a year or so ago.

Server-render Shadow DOM with declarative syntax ✨ Use <template shadowrootmode="open"> to create shadow roots in HTML. No JavaScript required for initial render. Perfect for SSR and web components. Learn more 👇 developer.mozilla.org/en-US/docs/Web…

@DamiDina Absolutely! 🙌

@MozDevNet This is actually my fav and it’s so performant too

Support dark mode with one CSS property 🌙 color-scheme tells the browser your page supports light, dark, or both. Form controls, scrollbars, and system colors adapt automatically. > :root { color-scheme: light dark; } Learn more 👇 developer.mozilla.org/en-US/docs/Web…

@chuksgabriel247 💪💪💪

@MozDevNet Great API, javascript all the way ... 💪

Parse and build query strings the easy way 🔗 URLSearchParams gives you a clean API for working with URL parameters. Get, set, append, delete, and iterate, no regex needed. Learn more 👇 developer.mozilla.org/en-US/docs/Web…

@MozDevNet »Somewhat controversially, the en-US locale uses the Oxford comma, while the en-GB locale does not.« I BEG YOUR PARDON?!

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 👇 developer.mozilla.org/en-US/docs/Web…

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 👇 developer.mozilla.org/en-US/docs/Web…

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 👇 developer.mozilla.org/en-US/docs/Web…

Fit images perfectly with object-fit 🖼️ Control how replaced content (images, videos) fills its container. cover, contain, fill, scale-down, or none. No more stretched or squished images. Learn more 👇 developer.mozilla.org/en-US/docs/Web…

Happening tomorrow at Mozilla Berlin! 🚨 Firefox, open source & the future of the web. 🎤 Firefox Mobile open source contributions 🗺️ Firefox Roadmap & upcoming features 🤝 Networking + raffle 🗓️ Apr 28 // 18:00 RSVP now! 👇 meetup.com/berlin-mozilla…