The navigator.language property is a string representing the preferred language of the user, usually the language of the browser UI. The navigator.languages property is an array of strings representing the user's preferred languages.

The list-style shorthand CSS property and the list-style-image, list-style-position, and list-style-type longhand properties set the position and appearance of a list item's marker.

The location global object represents the current page's address. You can use it to get the parts of the address (such as location.hostname or location.pathname) or navigate to another URL.

Map objects hold key-value pairs and remember the original insertion order of the keys.

The number type (and Number object) represents floating-point numbers, such as 42 or -4.201, while the Math API contains mathematical functions and constants. JavaScript can also represent boundless negative and positive values as Infinity or not-a-number as NaN (as in 0 * Infinity).

The @media CSS rule conditionally applies styles based on the output device type, its capabilities, and the user's preferences. Media queries are composed of an optional media type such as screen or print, and one or more mandatory media features, such as prefers-reduced-animations.

The <meta http-equiv="refresh"> HTML element and the equivalent Refresh HTTP header trigger a page reload or redirect. They apply only when the page is fully loaded, after other HTTP redirects or scripted redirects that might execute before the page is fully loaded.

The min-width, min-height, max-width, and max-height CSS properties set the minimum and maximum size of an element.

Mouse events, such as click, mousedown, or mousemove, fire when users interact with an input or pointing device such as a mouse, trackpad, or touchscreen.

The MutationObserver API watches for changes to the DOM tree and calls a callback function when DOM changes occur.

Some CSS color values can be referenced by name, such as red or limegreen. They stand in for specific RGB color values.

The window.navigator API is a generic global object, under which many other, more interesting APIs are located. It doesn't do anything interesting on its own.

The OES_element_index_uint extension for WebGL 1.0 contexts adds support for gl.UNSIGNED_INT types to WebGLRenderingContext.drawElements().

The OES_standard_derivatives extension for WebGL 1.0 contexts adds the GLSL derivative functions dFdx, dFdy, and fwidth.

The OES_texture_float extension for WebGL 1.0 contexts adds floating-point pixel types for textures.

The OES_texture_float_linear extension for WebGL 1.0 and 2.0 contexts adds linear filtering with floating-point pixel types for textures.

Objects in JavaScript are collections of key-value pairs.

The navigator.onLine property is a boolean for whether the browser is connected to some network (though not necessarily the internet). The online and offline events fire when the connection state changes.

The pageshow and pagehide transition events fire when a document loads or unloads due to a navigation, such as clicking on a link on a page or the back button in a browser.

The document.visibilityState and document.hidden properties tell you whether the page is visible to the user (for example, it's not minimized or in a background tab).

The physical CSS properties, top, right, bottom, and left, set the inset position of an element relative to the corresponding side of a container determined by the element's position property.

The position CSS property sets the origin position of an element to an element, the element's scrollport, or the viewport.

A promise represents an asynchronous operation which eventually succeeds or fails.

The RegExp object represents a regular expression, a notation for matching text patterns.

The position: relative CSS declaration offsets the position of an element relative to its position in the normal flow.

The <filter> SVG element applies custom effects such as color manipulation, blurring, or morphing to SVG elements.

The sandbox attribute for the <iframe> HTML element sets many security restrictions on the iframe, such as preventing form submissions or opening modal dialogs. Optional allow- values relax specific restrictions.

The window.screen property contains information about the screen of the output device that the referenced window is being rendered on.

CSS selectors match elements based on their type, attributes, and relationship to other elements. They define the specific elements to which a block of styles will be applied. This feature represents the oldest selectors of CSS.

Set objects store unique values of any type.