In this workshop we are building a web server application. Node.js provides all the functionality to do this, but at a very low level. You would need to make a lot of decisions about how to implement a server and then write that code and debug it. It’s a lot of work and it’s also work that you would have to do every time you wrote a web server application.

Wouldn’t it be great if someone had already done all that work?

Fortunately Node.js provides a way to publish code modules as packages. People publish packages that solve particular common problems that they find themselves doing over and over. So instead of you “re-inventing the wheel” every time, you can use other people’s packages and spend your time on what makes your application unique. The packages that you install and use in your application are called its dependencies.

You can find published packages on the NPM website, https://www.npmjs.com/. It currently has a little over half a million packages available.

Express is one such package. It takes the drudge work out of building a web server application, and we are going to install and use it to build our application.

Installing Express

We use the tool npm to install dependencies.

Run the following command in your terminal:

npm install express --save

This command does the following steps:

1. Looks up the express package
2. Identifies all the dependencies of express and then all the dependencies of those dependencies and so on
3. Downloads all the packages identified in step 2 and puts them in a directory called node_modules
4. Updates package.json to include express and a version number in the dependencies section

If you look in package.json now you’ll see a new section called dependencies with express listed in it:

"dependencies": {
    "express": "^4.16.1"
  }

Note: your version number for express may be different to the one above.

If you look in node_modules directory you will see a folder for each module. You will see around 50 folders because in addition to express it also installed all of the modules used by express and all of the modules that they use, and all of the modules that those ones use and so on. But it is smart enough to only download one copy of each.

So now we have express and all of its dependencies installed, let’s actually get on to writing some code.