janl/mustache.js — comment on commit 58c91c8c7d193b2c6e3dc3ebc4eb136a9bf1ea9f
File:  line 0
By AMorgaut:

It looks like JS engines made some improvements on String concatenations: http://stackoverflow.com/questions/7299010/why-is-string-concatenation-faster-than-array-join
The more explicit jsperf test looks to be this one: http://jsperf.com/join-concat/2
It shows that every browsers but Safari are now faster with direct String concatenation