The Object.groupBy() and Map.groupBy() static methods group values of arrays and iterables based on a function that returns a key for each value.

The i32.add, i32.sub, i32.mul, i64.add, i64.sub, and i64.mul operations extend constant expressions to include arithmetic.

The Promise.withResolvers() static method is an alternative to the Promise() constructor that returns both the promise and resolution functions. You can use this to access resolve and reject outside the scope of the executor function.

The transfer() and transferToFixedLength() methods of ArrayBuffer move a buffer from one context to another (for example, to a worker).

The checkVisibility() method checks if an element is potentially visible, with optional parameters for the kinds of visibility to check. For example, it checks whether the element has the style display: none, but can also check for visibility: hidden.

The shadowrootmode attribute on <template> creates a shadow root without the use of JavaScript. It is a declarative alternative to the attachShadow() method.

AVIF (AV1 Image File Format) is an image format based on the AV1 video format.

The Array.fromAsync() static method copies items from an async iterable object to make a new array.

The rect() CSS function creates a rectangle shape with insets from the edges of an element. The xywh() CSS function creates a rectangle shifted by an x and y distance. They can be used with clip-path and shape-outside.

The :has() CSS functional pseudo-class matches an element if any of the selectors passed as parameters would match at least one element.

The loading="lazy" attribute for <img> and <iframe> elements blocks loading the external resource until the user scrolls to that element's part of the page.

The reset() method clears a canvas to its initial state.

CSS nesting allows for shorter selectors, easier reading, and more modularity by nesting rules inside others.

The imagesrcset and imagesizes attributes with the rel="preload" attribute for the <link> HTML element starts fetching responsive images before they're found in the body of the document.

The cap CSS length unit corresponds to the height of Latin capital letters.

The counter-set CSS property creates (and optionally sets a value for) a counter, the numbers for a series of headings or ordered list items.

The createImageBitmap() global method creates an ImageBitmap object from a source such as an image, SVG, blob, or canvas. An ImageBitmap object represents pixel data that can be drawn to a canvas with lower latency than other types, such as ImageData.

The linear() easing function for animations and transitions interpolates linearly between the control points, and can be used to approximate complex easing functions, such as a bounce effect.

The preservesPitch property for <audio> or <video> adjusts the pitch of audio to sound more natural when the playback rate is faster or slower than the default.

The :dir() CSS functional pseudo-class matches elements by text direction, either right to left (rtl) or left to right (ltr).

The pow(), sqrt(), hypot(), log(), and exp() CSS functions compute various exponential functions.

The mask CSS property (and several longhand properties) partially or completely hides an element according to the shape and depth of an image.

The URL.canParse() static method checks whether a URL can be parsed into a valid URL object. It's an alternative to calling new URL() in a try … catch statement.

The scripting CSS media query sets styles based on whether scripting such as JavaScript is available. Values are enabled if scripting is available, initial-only if scripting is only available on page load (for example, printed content), or none.

The document.requestStorageAccess() method allows content in iframes to request storing and reading cookies and other site data, while the document.hasStorageAccess() method checks if such access is granted.

The navigator.userActivation API reveals whether the user has interacted with the page through an "activation" gesture such as a click, tap, or key press. User activation gated APIs (such as the fullscreen API) fail without user interaction, and this API allows you to predict such a failure.

The lh CSS length unit corresponds to the requested line height, the computed value of the line-height property. Some lines may be higher than this based on their content.

The rlh CSS length unit is a font-relative length relative to the line height of root element.

The :user-valid and :user-invalid pseudo-classes match form controls that have been marked as valid or invalid based on their validation constraints.

The fill-box, stroke-box, and view-box values for clip-path set an edge of the element's box to use as the clipping shape.