NPM – the Node.js package manager

Node.js by itself is a pretty basic system, being a JavaScript interpreter with a few interesting asynchronous I/O libraries. One of the things that makes Node.js interesting is the rapidly growing ecosystem of third-party modules for Node.js.

At the center of that ecosystem is NPM. While Node.js modules can be downloaded as source and assembled manually for use with Node.js programs, that's tedious and it's difficult to implement a repeatable build process. NPM gives us a simpler way; NPM is the de facto standard package manager for Node.js and it greatly simplifies downloading and using these modules. We will talk about NPM at length in the next chapter.

The sharp-eyed will have noticed that npm is already installed via all the installation methods discussed previously. In the past, npm was installed separately, but today it is bundled with Node.js.

Now that we have npm installed, let's take it for a quick spin. The hexy program is a utility for printing hex dumps of files. That's a very 1970 thing to do, but is still extremely useful. It serves our purpose right now in giving us something to quickly install and try out:

$ npm install -g hexy
/opt/local/bin/hexy -> /opt/local/lib/node_modules/hexy/bin/hexy_cmd.js
+ hexy@0.2.10
added 1 package in 1.107s

Adding the -g flag makes the module available globally, irrespective of the present-working-directory of your command shell. A global install is most useful when the module provides a command-line interface. When a package provides a command-line script, npm sets that up. For a global install, the command is installed correctly for use by all users of the computer.

Depending on how Node.js is installed for you, that may need to be run with sudo:

$ sudo npm install -g hexy

Once it is installed, you'll be able to run the newly–installed program this way:

$ hexy --width 12 ls.js
00000000: 636f 6e73 7420 6673 203d 2072 const.fs.=.r
0000000c: 6571 7569 7265 2827 6673 2729 equire('fs')
00000018: 3b0a 636f 6e73 7420 7574 696c ;.const.util
00000024: 203d 2072 6571 7569 7265 2827 .=.require('
00000030: 7574 696c 2729 3b0a 636f 6e73 util');.cons
0000003c: 7420 6673 5f72 6561 6464 6972 t.fs_readdir
00000048: 203d 2075 7469 6c2e 7072 6f6d .=.util.prom
00000054: 6973 6966 7928 6673 2e72 6561 isify(fs.rea
00000060: 6464 6972 293b 0a0a 2861 7379 ddir);..(asy
0000006c: 6e63 2028 2920 3d3e 207b 0a20 nc.().=>.{..
00000078: 2063 6f6e 7374 2066 696c 6573 .const.files
00000084: 203d 2061 7761 6974 2066 735f .=.await.fs_
00000090: 7265 6164 6469 7228 272e 2729 readdir('.')
0000009c: 3b0a 2020 666f 7220 2866 6e20 ;...for.(fn.
000000a8: 6f66 2066 696c 6573 2920 7b0a of.files).{.
000000b4: 2020 2020 636f 6e73 6f6c 652e ....console.
000000c0: 6c6f 6728 666e 293b 0a20 207d log(fn);...}
000000cc: 0a7d 2928 292e 6361 7463 6828 .})().catch(
000000d8: 6572 7220 3d3e 207b 2063 6f6e err.=>.{.con
000000e4: 736f 6c65 2e65 7272 6f72 2865 sole.error(e
000000f0: 7272 293b 207d 293b           rr);.});

Again, we'll be doing a deep pe into NPM in the next chapter. The hexy utility is both a Node.js library and a script for printing out these old-style hex dumps.