"NVM use" after entering each directory

.zshrc

# Run 'nvm use' automatically every time there's
# a .nvmrc file in the directory. Also, revert to default
# version when entering a directory without .nvmrc
#
enter_directory() {
if [[ $PWD == $PREV_PWD ]]; then
    return
fi

PREV_PWD=$PWD
if [[ -f ".nvmrc" ]]; then
    nvm use
    NVM_DIRTY=true
elif [[ $NVM_DIRTY = true ]]; then
    nvm use default
    NVM_DIRTY=false
fi
}

export PROMPT_COMMAND="$PROMPT_COMMAND; enter_directory"
prmptcmd() { eval "$PROMPT_COMMAND" }
precmd_functions=(prmptcmd)
# ...