Microsoft/TypeScript — pull request #460 by ahejlsberg (2014-08-15 14:55:28+00:00)
Title: Removed lookahead for simple arrow function expressions.

The parser currently performs a look-ahead on every expression that starts with an identifier to determine if an `=>` token follows. This commit reverts back to the original design of recognizing an expression consisting of a single identifier to the left of an `=>` token and then treating that identifier as a parameter list. This reduces the overall number of look-aheads performed by the scanner by over 30%.