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$ brew info nvm

nvm: stable 0.29.0, HEAD
Manage multiple Node.js versions
https://github.com/creationix/nvm
Not installed
From: https://github.com/Homebrew/homebrew/blob/master/Library/Formula/nvm.rb
==> Caveats
Please note that upstream has asked us to make explicit managing
nvm via Homebrew is unsupported by them and you should check any

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$ brew search nvm

convmv                     mvnvm                      nvm                      

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$ brew install nvm

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$ nvm

Node Version Manager

Usage:
  nvm help                              Show this message
  nvm --version                         Print out the latest released version of nvm
  nvm install [-s] <version>            Download and install a <version>, [-s] from source. Uses .nvmrc if available
  nvm uninstall <version>               Uninstall a version
  nvm use <version>                     Modify PATH to use <version>. Uses .nvmrc if available

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# never installed before
$ nvm install v4.2.1

# upgrading
$ nvm install v4.2.1 --reinstall-packages-from=<your_old_version>

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$ nvm alias default 4.2.1

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# install with global option because node.js has two kinds of package installs, 
# one is 'global' everything in the computer can use the global packages
# another one is 'local' only the designated area can use the local packages
# here we want babel (as a system-wide program) can be used from anywhere
$ npm install --global babel

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$ babel --version

5.8.29 (babel-core 5.8.29)

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$ node --version
v4.2.1

$ npm --version
3.3.10

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from Queue import Queue
from threading import Thread

'''
A single worker with queue and promise pattern
usage: worker.add_job(fn).then(callback_fn)

note: this might be anti-pattern
'''