Chrome 159 Release Notes

Makes the computed value of the background-* longhands keep the number of comma-separated values the author specified, instead of repeating or truncating it to the background-image layer count. Repeating and truncating are used-value behavior: "The computed values of the coordinating list properties are not affected by such truncation or repetition." This feature would implement the behavior defined in the https://drafts.csswg.org/css-values-4/ Appendix A.

Allow CSSImportRule.styleSheet to be nullable. The styleSheet attribute in CSSImportRule can be null if there is no associated CSS style sheet.

Allows authors to omit any descriptor in an @property rule and the corresponding optional members of CSS.registerProperty(). Omitted values default to universal syntax, inheritance, and the guaranteed-invalid initial value; invalid descriptors use normal CSS fallback behavior.

Expand the TextMetrics Canvas API to support selection rectangles, bounding box queries, and glyph cluster-based operations.

This new functionality should enable complex text editing applications with accurate selection, caret positioning, and hit testing. Additionally, cluster-based rendering facilitates sophisticated text effects such as independent character animations and styling.

For cross-origin resources, require that a resources is fetched with CORS for it to show its encoded/decoded body sizes as well as transferSize.

For encodedBodySize/decodedBodySize this would replace the Timing-Allow-Origin gate, while transferSize would require both.

Adds structured JavaScript access to SVG path data through three methods on SVGPathElement: getPathData() reads the path as an array of {type, values} objects containing each segment's command and numeric parameters. setPathData() updates the path from such an array, getPathSegmentAtLength() returns the segment at a specified distance along the path. These methods let developers inspect, edit, and construct paths without manually parsing or serializing the d attribute.

The optional getPathData({normalize: true}) setting simplifies path data to absolute move, line, cubic Bézier, and close commands (M, L, C, and Z). All three APIs operate on the base value of the d attribute, not CSS-computed or animated values.

Adds document.spellCheckCustomDictionary, which lets a page add words to and remove words from a per-document dictionary that the browser's spell checker consults alongside its built-in dictionaries. Matching words are no longer flagged as misspelled in that document, so sites with domain-specific vocabulary, such as product names, technical terms or proper nouns, can suppress false positives without asking users to edit their browser dictionary. The words last only for the document's lifetime and cannot be read back.

Adds the  WebTransportOptions.datagramsReadableType  constructor option. By default, incoming WebTransport Datagrams are exposed through a default  ReadableStream . Applications that require BYOB reading can request a readable byte stream by setting  datagramsReadableType: "bytes" .

Adds the modern WebTransport Datagram sending API.

WebTransportDatagramDuplexStream.createWritable() creates independent WebTransportDatagramsWritable streams. Each writable has mutable sendGroup and sendOrder attributes for expressing relative priority among queued WebTransport data in the same send group. Chromium currently applies this ordering among Datagram writables.

The implementation also reports the negotiated maximum outgoing Datagram payload size and discards oversized writes as required by the WebTransport specification.

WebTransport.getStats() provides asynchronous statistics for an existing connection: round-trip time measurements when available, an estimated sending rate when available, and counts of expired, lost, and dropped datagrams. Statistics remain accessible after the connection closes. Chromium does not currently expose connection byte or packet totals.

WebTransport already lets sites send data through WritableStreams. This feature will let applications group outgoing streams, prioritize data within each group, and view sending statistics for streams and groups, while preserving the ability to transfer streams.