Improving Oh My Zsh Startup Time with Lazy Loading

Using Oh My Zsh is usually a great experience. However, adding heavy plugins (like nvm) to load at startup time can really hurt performance. Luckily there’s a way to lazy load them.

A Simple Solution

# ~/.zshrc
plugins=(nvm git) # 1
zstyle ':omz:plugins:nvm' lazy yes # 2

source $ZSH/oh-my-zsh.sh # 3

1. Add the nvm plugin to your .zshrc file.
2. Enable lazy loading for the nvm plugin.
3. Make sure you source Oh My Zsh at the end.

This method reduced my shell startup time from ~1.5 s to ~200 ms. A huge improvement for a common action I perform many times daily.

However, I soon realised some of my projects had external dependencies that relied on commands like node and npm (and other package managers) to always be defined in the shell environment. This caused weird crashes, since lazy loading nvm means commands like node and npm only gets enabled when they first got used.

Conditionally Lazy Loading for Specific Directories

Adding an if statement to avoid lazy loading in specific directories:

# ~/.zshrc
plugins=(nvm git)

# This excludes any subdirectory of "/your-project/"
# =~ is used for RegExp matching.
if ! [[ $PWD =~ "/your-project/" ]]; then
  zstyle ':omz:plugins:nvm' lazy yes
fi

source $ZSH/oh-my-zsh.sh

Add more commands that should load nvm

In the documentation for nvm plugin, there are also other features that can be useful. For example, this is how to make sure npx and pnpx work even in new terminals.

zstyle ':omz:plugins:nvm' lazy-cmd npx pnpx

Hopefully this saves some time, allowing you move at the speed of thought 💭