I got tired of loading nvm every time in my fish shell, so this.

config.fish

# Requires bass and nvm
# bass: https://github.com/edc/bass
# nvm:  https://github.com/creationix/nvm

function nvm
  set -g NVM_LOADED "1"
  bass source ~/.nvm/nvm.sh ';' nvm $argv
end

function ensure_nvm_loaded
  if [ "$NVM_LOADED" != "1" ]
    set_color green
    echo "Loading nvm..."
    set_color normal
    nvm > /dev/null
  end
end

function node
  ensure_nvm_loaded
  command node $argv
end

function npm
  ensure_nvm_loaded
  command npm $argv
end

function ember
  ensure_nvm_loaded
  command ember $argv
end