NPX

 

In this post we will review NPX the Node Package Execute tool.

NPX is a command line util that is installed as part of the Node installation. Notice that this means that npx version is coupled with the node version.

The NPX temporary installs of packages that are used for a "script like"execution of a package. Instead of using npm to globally install a package and then run it, npx handles both.

The first step of NPX is to download the required package and its dependencies. The download target is:

~/.npm/_npx/<HASH>

The hash is based on the name and version of the package that NPX runs. Notice that the folder is never automatically removed, so once downloaded it will not be re-downloaded, that is unless we manually remove the cache folder or run a different version.

NPX however will not download to the cache folder if the package already exists in the current project node_modules folder, or if the package is globally installed.

To force NPX to download the latest version of a package and ignore any local or global installed version, we should specify the NPX flag --ignore-existing.

Common usages of NPX are:

npx create-react-app my-app
This will set the skeleton of a new react based application.

npx serve
This runs a file server on the current folder, enabling a quick review of the HTML files using a browser.

By default the NPX downloads the package, and the checks for "bin" entry in the package.json, which specifies the javascript file name to run. However we can manually determine the command to run using the syntax:

npx --package my-package my-command

In such case NPX would download the package and then look for the command under the bin element in package JSON and run it. Notice that we cannot run any javascript file using NPX, but only the predefined entries in the bin element. We can however, download the package using NPX, and the run any javascript file using node from the local NPX cache folder.