Keeping up with its biweekly cadence, Apple has pushed out new release for the developer-focused Safari Technology Preview. The latest release marks the sixth so far, and contains a number of new tweaks and improvements of note.

Safari Technology Preview release 6 is now available for download

If you're a developer who is interested in testing the preview out, here's the full list of what's new:


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


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

Web APIs

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

Web Inspector

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


  • Reduced flicker and jumpiness when entering and exiting fullscreen presentation mode

Bug Fixes

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

If you're unfamiliar, Safari Technology Preview is meant to give developers a way to experiment with new changes to the browser before they hit the general release. If you'd like to check it out, you can download the latest release directly from Apple.

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