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MDN Web Docs@developer· Jun 15

🆕 Introducing the MDN MCP server! Bring MDN's docs and browser compat data straight into your AI agent or IDE for accurate, up-to-date answers about the web platform. No more outdated guesses from training data. Learn more 👇 developer.mozilla.org/en-US/blog/introducing-mdn-mcp-server/

MDN Web Docs@developer· May 18

Ever wish HTTP status codes were easier to remember? 🖼️ Check out this MDN cheatsheet that pairs each status code with an emoji to help you visualize what each one means, from 200 OK ✅ to 418 I’m a teapot 🫖 Check it out 👇

A colorful infographic titled “MDN HTTP Code Cheatsheet with Emojis.” It categorizes HTTP status codes using emoji-enhanced lists grouped by status code classes.

MDN Web Docs@developer· May 18

🦊 Firefox 150: web extensions can now use the Web Authentication API. Extensions can create and retrieve WebAuthn credentials for any domain covered by their host permissions. Read Now 👇 developer.mozilla.org/en-US/docs/...

Firefox 150 release notes feature a minimalist design with soft colors, highlighting new capabilities for web extensions.

MDN Web Docs@developer· May 11

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

Code snippet showcasing CSS Subgrid implementation with defined grid properties for a main grid, items, and sub-items.

MDN Web Docs@developer· May 11

🆕 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/...

Dark-themed code snippet showing URLPattern examples on MDN: two JavaScript blocks matching "/books" and "/books/:id" with console.log outputs.

MDN Web Docs@developer· May 10

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

JavaScript code demonstrating `Promise.allSettled()` handling fulfilled and rejected promises, along with results logging output.

MDN Web Docs@developer· May 8

📬 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 👇 developer.mozilla.org/en-US/docs/...

Code snippet demonstrating the use of Object.hasOwn() in JavaScript to check property existence in various scenarios.

MDN Web Docs@developer· May 8

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

Code snippet showcasing various CSS `backdrop-filter` functions like blur, brightness, contrast, and saturation against a blue background.

MDN Web Docs@developer· May 8

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

Code snippet illustrating CSS sibling selection with `li:has(+ li:last-of-type)` and style rules for color and font weight.

MDN Web Docs@developer· May 7

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

The graphic displays the syntax for the `caretPositionFromPoint()` function in a code snippet format against a blue background.

MDN Web Docs@developer· May 7

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

Code snippet demonstrating a simple popover with a toggle button, showcasing HTML attributes for functionality.

MDN Web Docs@developer· May 6

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

Code snippet demonstrating error handling in JavaScript using `try`, `catch`, and `Error.cause` for maintaining context during rethrowing.

MDN Web Docs@developer· May 6

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

CSS snippet detailing the `content-visibility` property with keyword and global values for efficient rendering practices.

MDN Web Docs@developer· May 5

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

Code snippet demonstrates using `ResizeObserver` to adjust element width dynamically based on its content size.

MDN Web Docs@developer· May 5

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

Syntax for `requestIdleCallback()` shown on a dark background, highlighting its parameters for managing browser idle time efficiently.

MDN Web Docs@developer· May 4

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/...

Code snippet demonstrating temporal date precision in JavaScript, highlighting differences in epoch milliseconds output.

MDN Web Docs@developer· May 1

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/...

Code snippet demonstrating the `toSorted()` method, showcasing sorting of arrays without mutating the original arrays.

MDN Web Docs@developer· Apr 30

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/...

CSS code snippet demonstrating styles for input and select elements with the :focus-visible pseudo-class for improved accessibility.

MDN Web Docs@developer· Apr 30

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/...

Code snippet demonstrating chaining of multiple ReadableStreams with TransformStream in a JavaScript context.

MDN Web Docs@developer· Apr 29

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/...

Code snippet demonstrating the syntax for the HTTP Clear-Site-Data header, including single, multiple, and wildcard directives.

MDN Web Docs@developer· Apr 29

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/...

Code snippet demonstrates a JavaScript function using `queueMicrotask()` to manage data loading and caching with event dispatching.

MDN Web Docs@developer· Apr 28

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/...

Code snippet demonstrating the use of Intl.ListFormat to format lists in different styles and types in JavaScript.

MDN Web Docs@developer· Apr 28

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/...

Syntax for the CSS property `object-fit`, showing values like contain, cover, fill, and scale-down on a dark background.

MDN Web Docs@developer· Apr 27

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/...

Code snippet demonstrating usage of URLSearchParams for manipulating URL parameters, including getting, setting, and appending values.

MDN Web Docs@developer· Apr 27

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! 👇 www.meetup.com/berlin-mozi...

Event announcement for Tech Talks at Mozilla in Berlin on April 28, 2026, featuring talks, networking, and a raffle.

MDN Web Docs@developer· Apr 24

Transform iterators without converting to arrays 🔄 Iterator helpers like .map(), .filter(), .take(), and .drop() work lazily on any iterable. Process data efficiently without intermediate arrays. Learn more 👇 developer.mozilla.org/en-US/docs/...

Code snippet illustrating the creation of a custom iterator class in JavaScript, showing methods for object iteration.

MDN Web Docs@developer· Apr 24

🦊 Firefox 150 is here! What's new? 🎨 color-mix() accepts multiple colors 🎥 New :playing, :paused, :muted media pseudo-classes 📜 animation-range-start/end for scroll animations ♿ ariaNotify() for screen reader support and more... Release notes 👇 developer.mozilla.org/en-US/docs/...

Firefox 150 release notes highlighted with a soft background, featuring announcement text and a call to action to read more.

MDN Web Docs@developer· Apr 22

Transform key-value pairs back into objects ↩️ Object.fromEntries() is the inverse of Object.entries(). Convert Maps, arrays, or URLSearchParams directly into plain objects. Learn more 👇 developer.mozilla.org/en-US/docs/...

JavaScript code demonstrates using `Object.fromEntries()` to convert a Map into a plain object with key-value pairs.

MDN Web Docs@developer· Apr 22

Use gap in flexbox, no more margin hacks 📐 The gap property works in flexbox, grid, and multi-column layouts. Set consistent spacing between items without affecting outer edges. Learn more 👇 developer.mozilla.org/en-US/docs/...

CSS code snippet shows various uses of the gap property in flexbox and grid layouts for consistent spacing between items.

MDN Web Docs@developer· Apr 21

Read and build form data with the FormData API 📋 Construct form submissions programmatically, including file uploads. Works with fetch() for modern form handling. Learn more 👇 developer.mozilla.org/en-US/docs/...