Safari Technology Preview release 6 is now available for download

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.

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{.nofollow} directly from Apple.

Dan Thorp-Lancaster