Release Notes for Safari Technology Preview 21

Safari Technology Preview Release 21 is now available for download for macOS 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 209803-210274.


  • Enabled concurrent garbage collection (r209694)
  • Enabled <script type="module"> (r210016)
  • Added support for the global property on the global object (r210052)

Fetch API

  • Improved console logging when loading resources (r209917)

IndexedDB 2.0

  • Improved the speed of IDBIndex.get() (r209824)
  • Improved the speed of iterating cursors (r209977)


  • Updated the syntax of the prefers-reduced-motion media query (r209842)
  • Fixed CSS scroll snap to work when scrollbar is hidden (r210117)
  • Fixed column overflows when text-align: justify is combined with word-spacing (r209910)


  • Fixed a font variations bug exposed by the Skia font (r210054)
  • Fixed an issue with multicolumn inside SVG <foreignobject> (r210035)
  • Fixed a floating element overlapping the marker within an <li> (r210239)


  • Fixed changing focus to modal dialogs when one appears (r210265)
  • Changed VoiceOver to read table headers that are not visible onscreen and do not use have an aria-hidden attribute (r210150)


  • Fixed firing Input Events with null inputTypes and no data when changing the text direction (r209976)
  • Fixed handling key generation with an empty challenge string (r209822)
  • Fixed focus for label elements with a tabindex value of 0 or higher (r210267)
  • Fixed side effects while resetting form elements (r209990)
  • Corrected setting the original URL of a download request with target="_blank" (r210083)
  • Updated HTML form validation bubbles to be dismissed on navigation (r209941)

Web Inspector

  • Allow simple await expressions to be run in the console (r210033)
  • Fixed Computed Styles to correctly show the Container Regions section for regions content flows into (r210250)
  • Fixed jumping to the definition of a custom element (r209855)
  • Fixed uncommenting to enable CSS rules of pseudo-elements in the Styles sidebar (r210110)
  • Updated CodeMirror to add support for the async and await keywords along with other ECMAScript 2017 features (r210032)
  • Fixed repositioning Timeline graph elements when resizing the window (r210046)
  • Fixed zooming in the Timeline to zoom where the cursor is located (r209834)
  • Improved console for narrow widths (r209882)
  • Modernized the find banner UI (r209921)
  • Updated keyword completions in Web Inspector for the new scroll snapping CSS properties (r210036)


  • Allowed HTTPS URLs to match HTTP script-src expressions for Content Security Policy (r209821)

Bug Fixes

  • Fixed a Safari crash that occurs when deleting a Chinese character typed after an image (r209957)
  • Selecting when zoomed in no longer jumps around (r210147)