We got that error in Chrome. The code which is underlined red in the sources tab says `for(void 0 in n)`. See attached code files of it working in v2.6.3 and the error in v2.8.3. [v2.8.3-ERROR.js.txt](https://github.com/mishoo/UglifyJS2/files/810828/v2.8.3-ERROR.js.txt) [v2.6.3-OK.js.txt](https://github.com/mishoo/UglifyJS2/files/810829/v2.6.3-OK.js.txt)