A set of bash/zsh functions that provide simple virtual environment capabilities for node.

nenv.sh

#
# A set of bash/zsh functions that provide simple virtual environment
# capabilities for node. To install, just copy this file into your home
# directory and add the following to your .bashrc or .zshrc file:
#
# if [[ -f "$HOME/.nenv" ]]; then
#     source "$HOME/.nenv"
# fi
#
# What this script provides is a set of functions that are activated whenever
# you cd into a new directory. If that directory contains a node_modules folder,
# it will add all of the installed modules' bin folders to the PATH. Once you
# exit the folder, the PATH is returned back to its original state.
#
# In addition, if a .activate file is found in the directory, it will source
# it upon entry. Likewise, if a .deactivate file is found, it will source it
# upon exit. These files allow you to do extra setup/teardown to your
# environment as needed.
#

# Checks that the child directory is a subdirectory of the parent
is_subdirectory() {
    local child="$1"
    local parent="$2"
    if [[ "${child##${parent}}" != "$child" ]]; then
        return 0
    else
        return 1
    fi
}

# Activates a new environment
activate_env() {
	# Exit the function if npm isn't installed
	if ! npm -v >/dev/null 2>&1; then
		return 1
	fi

    # Check if the directory we've cd'ed into is a node environment directory
    # (i.e., it contains a node_modules folder) and that a node envrionment
    # does not already exist before creating a new one.
    if [ -d "node_modules" ] && [ -z "$_ENV_DIR" ]; then

        # Save the old PATH variable so we can revert back to it when we leave
        # the environment
        export _OLD_PATH="$PATH"

        # An environment is essentially nothing more than an environment
        # variable (_ENV_DIR) pointing the parent directory of our node
        # environment. Create the variable and point it to $PWD.
        export _ENV_DIR="$PWD"

        # Add the bin folder for all local NPM installs to the PATH
        export PATH="$(npm bin):$PATH"

        # If an activation script exists, execute it
        if [ -e ".activate" ]; then
            source .activate
        fi
    fi
}

# Deactivates the current envrionment
deactivate_env() {
    # Make sure that an envrionment does exist and that the new
    # directory is not a subdirectory of the envrionment directory
    if [ -n "$_ENV_DIR" ] && ! is_subdirectory "$PWD" "$_ENV_DIR"; then

        # Run the deactivation script if it exists
        if [[ -e "$_ENV_DIR/.deactivate" ]]; then
            source "$_ENV_DIR/.deactivate"
        fi

        # Revert back to the original PATH
        export PATH="$_OLD_PATH"

        # Destroy the environment
        unset _ENV_DIR
        unset _OLD_PATH
    fi
}

env_cd() {
    builtin cd "$@" && deactivate_env && activate_env
}

alias cd="env_cd"