Safari Technology Preview Release 8 is now available for download for both macOS Sierra beta 2 and OS X El Capitan. If you already have Safari Technology Preview installed, you can update from the Mac App Store’s Updates tab. Release 8 of Safari Technology Preview covers WebKit revisions 202085–202612. JavaScript Achieved 100% ECMAScript 2015 (ES6) support by adding back Symbol.isConcatSpreadable