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Node.js and Package Managers

Introduction​

You are very familiar with Javascript by now, and you may notice that we can only run Javascript in our browser using the <script> tag. What if we want to write scripts using Javascript and run them using the local machines, just like how python is.

This is where Node comes into play. It is a JavaScript runtime engine built on Chrome's V8 Javascript engine that allows you to run JavaScript even without a browser. This means that you are able to do a lot more with JavaScript: managing local files, connecting and setting up a server, and much more.

Learning Objectives​

  1. How npm & node works
  2. Create Backend APIs using Node & Express
  3. How to make API calls using axios
  4. File system with node & express
  5. Understand cookies

Getting Started​

Let's start by creating a folder for us to put our code in. Let's call this folder example and then let's cd` into it using the console.

mkdir example
cd example

NPM​

With the ability to run JavaScript locally on our machine (with the help of Node) and the contribution of a rich number of packages from a large community, the possibilities for JavaScript are endless!

To manage many of the packages that give Node its most powerful abilities, we use NPM. Node package manager (NPM) is a place where you can find and download node packages.

npm

Installing Node​

Go to https://nodejs.org/en/ to install node.js for free.

Let us confirm that you have correctly downloaded Node.js and npm.

In the terminal, type

node -v
npm -v

If both lines output the version number then we are good.

Now, let us install out first package. The remainder of this example we will be using Axios to make HTTP requests as necessary, so let us install Axios.

Navigate to the folder where we are storing our project, in this case example/ while there, type the following command:

npm init -y
npm install axios

The npm init command is used to create a new npm package, essentially every node script that we will write can be treated as a npm package. The -y flag just skip all the configuration step and creates a most basic npm package with all default settings.

Now when we list the files in our example/ directory, we should see three things:

  • node_modules folder
  • package.json file
  • package-lock.json file (optional)

Essentially, each of these helps npm organize the packages we installed. In the node_modules folder is where we can find our actual packages. Many times, our node_modules file grows incredibly large and can take up quite a bit of space. It is discouraged to go directly into the node_modules, instead, npm provides a variety of utilities which we can use to keep our projects clean and efficient. I won't go into them here, but as you develop, you will run across them or you can read the docs here. The other file is the package.json file. The package.json file is the file which record and defines the top-level packages and dependencies for our project. package-lock.json is a similar idea but with some nuances, you do not need to worry about those.

Hello World​

Now let's move back to Node for a second. Let's create a file called helloworld.js in the example/ folder. Enter console.log("hello world.") in the file.

You can run any node file by using the Node command.

node helloworld.js

The console should print "hello world." and then exit.

JS in Browser vs. Node.js​

Node in browser and Node.js are technically the same form of JavaScript. Both run on the browser's JavaScript engine, usually Chrome V8. However, there are some fundamental difference which make Node.js just different enough to be annoying. The most prominent difference is that Node.js uses the require module to import other modules which define functionality. All Node projects are organized into modules, and we use require to import them. For example, the following code imports Axios, a package commonly used to make HTTP requests.

Another difference is that since there is no web page to be manipulated, there is no document object for Node.js, which means that DOM manipulation cannot be carried out in Node.js (with the help of some packages, it can).

Since Node is a server side language, it can interact with the local file system easily, it also provides ways to setup a server with ease.

If you are familiar with the fetch function in JS, there is no fetch function in Node. You can use the http package or some other third party package to handle sending a request.