fnvm is some hacky method that makes nvm much faster in cygwin.
In cygwin, nvm makes bash slower. even it takes 2~10 second to initialize
fnvm using ~/.nvmrc.cached which created by user and contain cached node version to set PATH directly without calling nvm's version resolver which is very slow due to checking system installed nodejs and iojs, resolving all of installed nodes.

It also includes auto version changing when change cwd

If nvm is not installed, install nvm first

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.3/install.sh | bash

Next, install fnvm

git clone https://github.com/qwreey75/fnvm.git ~/.fnvm --depth 1
source ~/.fnvm/fnvm.sh; FNVM_DIR=~/.fnvm fnvm_update

Done! If you want update fnvm, simply type fnvm_update

you can insert these setting above source $HOME/.nvm/fnvm/fnvm.sh; fnvm_init in your rc file

export FNVM_DISABLE_CD="no" # If this value is "yes". auto version changing will be disabled

[ -s "$NVM_DIR/bash_completion" ] && . "$NVM_DIR/bash_completion" # This loads nvm bash_completion

In cygwin, Normal nvm takes ~2 second, but fnvm only takes 0.2 second! Almost ten times faster then normal nvm.