Hold object references without preventing garbage collection 🗑️

`WeakRef` lets you reference an object while allowing it to be GC’d if nothing else holds a strong reference. Use for caches, and pair with FinalizationRegistry.

Learn more 👇
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakRef

🆕 Animate elements from display: none

CSS `@starting-style` lets you define the initial style for elements entering the page, enabling enter animations without JavaScript.

⋅ Combine with transition
⋅ Works with popover and dialog

Learn more 👇
https://developer.mozilla.org/en-US/docs/Web/CSS/@starting-style

Measure your own code performance precisely ⏱️

`performance.mark()` and `performance.measure()` let you instrument JavaScript with high-precision timings.

Learn more 👇
https://developer.mozilla.org/en-US/docs/Web/API/Performance/mark

Creating a resolvable Promise just got cleaner 🧹

`Promise.withResolvers()` returns { promise, resolve, reject }
No more wrapping logic inside the constructor.

Learn more 👇
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/withResolvers

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

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

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

Stop scroll chaining with overscroll-behavior 🛑

Prevent modals and sidebars from accidentally scrolling the page behind them.
⋅ Works on any scrollable element
⋅ Also controls the bounce effect on mobile

Learn more 👇
https://developer.mozilla.org/en-US/docs/Web/CSS/overscroll-behavior

Access characters from the end of a string with .at() ✨

str.at(-1) gets the last character, no more str[str.length - 1] gymnastics.

Works on strings, arrays, and typed arrays.

Learn more 👇
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/at

🆕 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