First API With Node.JS and Express

Here we see those steps

1. Create a Project
2. Install Dependencies
3. Create a Server
4. Create Get Endpoint
5. Create Post Endpoint

Create a Project

To create a Node.JS project you need to install node/npm (or yarn), on you machine.

Please download here https://hilt.onl/nodejs .

With all set up create a folder with your project name, e.g. Test, here we will use npm as a package manager. Use the terminal of you preference to setup the project, here I’ll use Linux

~/Projects/Test$

Inside the folder type npm init, this create a default package.json with your project properties, the command will ask you some arguments

package name: (test) 
version: (1.0.0) 
description: This is my description
entry point: (index.js) 
test command: 
git repository: 
keywords: 
author: Me
license: (ISC)

When you finish, it’s will write a new package.json which contains the specified arguments, as follow

About to write to /home/iMaUser/Projects/Test/package.json:
{
  "name": "test",
  "version": "1.0.0",
  "description": "This is my description",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Me",
  "license": "ISC"
}

Is this OK? (yes)

Confirm, and see the package.json inside the project folder. A package.json is where you describe your project to npm, how to start, your project scripts, dependencies and arguments. And also with this you can use the follow command

npm install

to install all dependencies previously saved.

Let’s create a empty file called index.js, where the npm starts the project, in next steps we will create some interesting things to interact.

Install Dependencies

We need to tell which dependencies our project uses, first we will install a dependence called Express, globally, so we can use some command lines tools in the project. Please run it with admin rights, cause this will install some global commands.

npm install -g express-generator

And now we need to tell npm that we also use the express inside the project as follow

npm install express --save

After this the follow will be add on package.json

"dependencies": {
    "express": "^4.17.1"
  }

Create a Server

Let’s code, open the index.js and use the code

//Tell that we REQUIRE use the express module 
const express = require("express");
//Start express
const app = express();
//Listen to port 3000
app.listen(3000, () => {
 console.log("It's Works. Running on port 3000");
});

So starts the application using the command

node index.js

And it’s will shows

It's Works. Running on port 3000

When we access it through this address http://localhost:3000, express says

Cannot GET /

Because we don’t have any endpoint point to “/”.

Create Get Endpoint

We have a server, but the server does nothing without some endpoints, now we can create a GET request, as follow

//GET endpoint on echo path
//Request, response
app.get("/echo", (_req, res) =>{
    res.send("echo, echo,  echo ...")
});

And start server again

node index.js

Go to follow address http://localhost:3000/echo, and we can see the message we returned to this path

echo, echo, echo ...

If you change the

res.send("echo, echo,  echo ...")

You can customize the output.

We have a GET request, but I want to to send and read a parameter from URL. How can I do it?

Change the code

//GET endpoint on echo path
//Request, response
app.get("/echo", (req, res) =>{
 //Query is a parameter from the url
 let name = req.query.name
 //Don't has a name?
 if(!name){
    res.send("echo, echo,  echo ...");
 //has a name
 }else{
    res.send("Echo? Hello " + name + "!");
 }
});

Start the server

node index.js

When we access http://localhost:3000/echo, we have the same result, but if we put the parameter http://localhost:3000/echo?name=Hilton, we see the new send works.

Echo? Hello Hilton!

Create Post Endpoint

To create a POST, we need a body parser, add line in bold

//Start express
const app = express();
//Parse body as it is, you can use .json .text, and others
app.use(express.json())
//Listen to port 3000

It’s says all my request will use json, so it’s parse the data send to json format, you also can specifies by resource like this

app.post("/echo", express.json(), (req, res)

Also you can specifies your own format.

Change the code adding this

app.post("/echo", (req, res) => {
   //Sends to console the received body
    console.log(req.body);
    //Send a OK status
    res.sendStatus(200)
});

Start the server

node index.js

In this example we will send on JSON format using cURL

curl -H 'Content-Type:application/json' -d '{"name":"My body"}' http://localhost:3000/echo

The output on server will be the follow

~/Projects/Test$ node index.js 
It's Works. Running on port 3000
{ name: 'My body' }

And we finish a simple API server, change the code and please, send me feedback!

See you in the next post!