Ioannis Poulakas

Software Developer

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How to speed up shell load while using NVM

22 Feb 2020

If you are developing any application that depends on NodeJS, using NVM (Node Version Manager) is highly recommended.


The only downside of NVM is that it significantly slows down shell prompt initialization while using the default settings.

Here is how it is configured by default for bash:

# Load NVM
export NVM_DIR=~/.nvm
[[ -s "$NVM_DIR/" ]] && source "$NVM_DIR/"

And here is how bad it performs:

$ time source ~/.bash_profile

real 0m0.478s
user 0m0.291s
sys  0m0.198s

First solution, lazy load NVM

There are simple bash scripts that can lazy load NVM during the first invoke of the nvm command. Of course catching nvm is not enough, script should also be checking for npm, node, npx, and any other global package that is installed. Also that very first load will be equally slow to the timings shown above.

Here is how a minimal bash script would look like for capturing the node command and lazy loading NVM:

lazy_load_nvm() {
  unset -f node
  export NVM_DIR=~/.nvm
  [[ -s "$NVM_DIR/" ]] && source "$NVM_DIR/"

node() {
  node $@

The node function above can be replicated for capturing the other executables of choice, just remember that they should be included on the unset command as well.

Second solution, load NVM in a much faster way

NVM while loading up is checking which node version to auto-use based on .nvmrc or a similar configuration file. And this exact check is the one that takes most of the time to complete.
Good news is that there is a flag for skipping this check.
However without an autoloaded node version, there should still exist a fallback to a preferred version for fast access.

Putting those two together on the bash init is as simple as:

# Add default node to path
export PATH=~/.nvm/versions/node/v12.16.1/bin:$PATH

# Load NVM
export NVM_DIR=~/.nvm
[[ -s "$NVM_DIR/" ]] && source "$NVM_DIR/" --no-use

Let's measure the startup time:

$ time source ~/.bash_profile

real 0m0.051s
user 0m0.031s
sys  0m0.018s

Boom, almost half a second faster!

If a project is using a different node version than the one declared on the bash init, then it's just a matter of remember running nvm use before issuing any other node related commands.
Updating the default version via NVM, would also require updating manually the version on bash init.


I personally prefer the second solution, as I am usually working with the latest LTS node version on active projects. Thus I rarely have to invoke nvm use manually. Time saved overall from spawning shell instances definitely worths it.

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