Heroku runs plv8 v1.4.2 (checked on 1st April 2016). On OSX it's easiest to install v1.4.3 since that allows V8 3.15 which is available via homebrew. (1.4.2 wants V8 3.14.5).
brew install v8-315 pip install pgxnclient LIBRARY_PATH="/usr/local/opt/v8-315/lib" CPATH="/usr/local/opt/v8-315/include" pgxnclient install plv8=1.4.3
To test it worked:
$ psql # CREATE EXTENSION plv8; CREATE EXTENSION # DO $$ plv8.elog(NOTICE, "Hello World") $$ LANGUAGE plv8; NOTICE: Hello World DO # DROP EXTENSION plv8; DROP EXTENSION #