Release Notes for Safari Technology Preview 57

Safari Technology Preview Release 57 is now available for download for macOS High Sierra. If you already have Safari Technology Preview installed, you can update from the Mac App Store’s Updates tab. This release covers WebKit revisions 231553-232108.

This version of Safari Technology Preview will no longer run on macOS Sierra. To continue testing or living on the latest enhancements to Safari and WebKit, please upgrade to macOS High Sierra.


  • Added support for Intl.NumberFormat().formatToParts() (r231867)
  • Changed to throw SyntaxErrors for runtime generated regular expressions with errors (r231939)
  • Implemented BigInt support for *, /, and == operations (r231733, r231886, r231629)
  • Improved specification compliance for Internationalization APIs (r231740)
  • Improved the speed of Object.assign for final objects (r231687)


  • Exposed Web Animations CSS integration as an experimental feature (r231798)
  • Fixed a bug where animation-play-state:paused causes very high cpu load because of a style invalidation loop (r231794)

Storage Access API

  • Extended the lifetime of cookies on successful user approval (r231684)


  • Added initial support for the Cross-Origin-Options HTTP response header (r231622, r231654)
  • Changed Cross-Origin-Options:deny and Cross-Origin-Options:allow-postmessage to prevent getting navigated by cross-origin scripts (r231911)
  • Changed X-Frame-Options:SAMEORIGIN to check all ancestor frames (r231730)


  • Enabled the modern EME API by default (r231903)
  • Fixed media continuing to load after rendered invisible (e.g. removed from DOM; scrolled off screen) (r231817)
  • Improved NowPlaying using the element "title" attribute when available (r231866)


  • Changed the accessiblility name provided for a node to simplify the whitespace when using innerText (r231627)
  • Excluded hidden nodes which are not directly referenced from participating in name or description content (r231620)
  • Ensured listbox and combobox roles embedded in labels participate in name calculation (r231778)
  • Exposed the primary screen height through the AX API (r231937)
  • Fixed a bug with VoiceOver causing <iframe> scrolling focus jumping (r231628)
  • Fixed VoiceOver to manually focus or read dialog paragraph description text inside the modal in role=dialog elements with aria-modal=true (r231720)


  • Fixed a crash that happens if a browsing context’s cookies are requested prior to an initial navigation (r232031)
  • If the network or storage process crashes, terminate the automation session to avoid undefined behavior (r232028)
  • Automation.getBrowsingContext now returns the same window origin as window.screenX and window.screenY (r231769)

Web Inspector

  • Added rulers and guides to the Canvas tab (r231819, r231881)
  • Changed the Canvas tab to not automatically select a recording when viewing a canvas (r231773)
  • Improved the placement logic for the element details popover that is shown during Inspect Element mode (r231838)
  • Calculating the visual effect of each Canvas action is now off by default for performance reasons. (r231981)