Release Notes for Safari Technology Preview 6

Safari Technology Preview Release 6 is now available for download. If you already have Safari Technology Preview installed, you can update from the Mac App Store’s Updates tab. Release 6 of Safari Technology Preview covers WebKit revisions 201084–201541.


  • Added support for trailing commas in function parameters per draft ECMAScript spec (r201488)
  • Improved RegExp matching when the result array becomes large (r201451)
  • Made RegExp throw an exception instead of a crash when matching deeply nested subexpressions (r201412)
  • Made TypedArray.prototype.slice no longer throw an exception if no arguments are provided (r201364)
  • Improved performance of TypedArray access by 30% in the 64-bit low-level interpreter (r201335)
  • Fixed a regression where String.prototype.replace would fail after being used many times with different replace values (r201254)
  • Improved integer to float conversion code generation in the B3 JIT Compiler (r201208)
  • Fixed arrow functions as default parameter values so they capture this properly (r201122)


  • Added support for normal keyword value per draft CSS Box Alignment Module Level 3 spec (r201498)
  • Updated the parsing of CSS Grid’s fixed-size per the draft spec (r201399)
  • Made elements with backdrop-filter clip when used with clip-path or mask (r201374)
  • Made changing border-color and border-width on table cells with border-collapse: collapse repaint properly (r201296)
  • Fixed overflow: hidden so it always repaints clipped content when overflow changes (r201407)

Web APIs

  • Started allowing empty strings in the FontFace constructor and parse them as if they are omitted (r201421)
  • Stopped firing a popstate event with a null state when navigating back to a stateless cached page (r201310)
  • Started allowing custom drag-and-drop even without placing data in the pasteboard (r201227)

Web Inspector

  • Made the split console stay closed when using Inspect Element context menu item (r201222)
  • Fixed a regression where CSS properties modified via JavaScript didn’t update in the DOM tree or Styles sidebar (r201192)
  • Improved garbage collection time by 2x when recording heap snapshots (r201520)
  • Made heap snapshot views remove objects that have been garbage collected (r201183)
  • Corrected how transitively dominated objects in heap snapshots display their retained size (r201477)
  • Made ShadowChicken properly handle when the entry stack frame is a tail deleted frame (r201465)
  • Added indicators to show nesting levels for DOM elements in the Elements tab (r201454)
  • Fixed a regression where WebSQL databases were no longer shown in the Storage tab on first open (r201409)
  • Improved load time of Web Inspector by profiling with Web Inspector (r201245)
  • Fixed resuming the debugger after breaking on an exception inside a Promise callback (r201211)
  • Fixed the main resource not showing up in the Debugger tab sidebar after a reload (r201210)


  • Reduced flicker and jumpiness when entering and exiting fullscreen presentation mode (r201405, r201474, r201530)

Bug Fixes

  • Fixed scrolling on iTunes Connect pages (r201218)
  • Fixed autocorrection so it is easier to type contractions and email addresses (r201490)
  • Fixed a crash during font download failure after garbage collection (r201358)
  • Reverted the change to ignore clicks inside button elements when the mouse moves, due to a regression (r201292)
  • Fixed a regression that broke Zoom In (⌘+) on pages (r201090)