Extend nvm function for upgrade command

zsh-nvm.plugin.zsh

@@ -1,5 +1,11 @@
 [[ -z "$NVM_DIR" ]] && NVM_DIR="$HOME/.nvm"
 
+_zsh_nvm_rename_function() {
+  test -n "$(declare -f $1)" || return
+  eval "${_/$1/$2}"
+  unset -f $1
+}
+
 _zsh_nvm_has() {
   type "$1" > /dev/null 2>&1
 }
@@ -25,6 +31,9 @@ _zsh_nvm_install() {
 }
 
 nvm_update() {
+  echo 'Deprecated, please use `nvm upgrade`'
+}
+_zsh_nvm_upgrade() {
   local installed_version=$(cd "$NVM_DIR" && git describe --tags)
   echo "Installed version is $installed_version"
   echo "Checking latest version of nvm..."
@@ -41,5 +50,24 @@ nvm_update() {
 # Install nvm if it isn't already installed
 [[ ! -f "$NVM_DIR/nvm.sh" ]] && _zsh_nvm_install
 
-# If nvm is installed, source it
-[[ -f "$NVM_DIR/nvm.sh" ]] && source "$NVM_DIR/nvm.sh"
+# If nvm is installed
+if [[ -f "$NVM_DIR/nvm.sh" ]]; then
+
+  # Source nvm
+  source "$NVM_DIR/nvm.sh"
+
+  # Rename main nvm function
+  _zsh_nvm_rename_function nvm _zsh_nvm_nvm
+
+  # Wrap nvm in our own function
+  nvm() {
+    case $1 in
+      'upgrade')
+        _zsh_nvm_upgrade
+        ;;
+      *)
+        _zsh_nvm_nvm "$@"
+        ;;
+    esac
+  }
+fi