Creating a Basic Express API

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Scenario

We need to create an express endpoint /api/hello/:name . If :name is fireflysemantics it should return this JSON object:

{
    "name": "fireflysemantics",
    "greeting": "Hello there Fireflysemantics, it's nice to meet you!"
}

Note that the name must be capitalized in the greeting.

We will be using Linux command line tools to illustrate how they can be used, but everything can be done in a text editor like VS Code as well.

Approach

Setup

Create a project directory:

mkdir api
cd api

Initialize the project:

npm init -y

Initialize git:

git init

Ignore node_modules when committing code:

touch .gitignore
vi .gitignore

Add node_modules to .gitignore with vi .

Install express:

npm i express

After the install package.json should look like this ( cat package.json ):

{
  "name": "api",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "express": "^4.17.1"
  }
}

The dependencies section shows us that express is installed.

Implementation

Create the javascript file hello-api.js :

touch hello-api.js

Make the following edits hello-api.js so that it contains the following.

//Import express
const express = require('express')
//Create the express app
const app = express()
//Set the port
const port = 3000
//Test a hello get request endpoint
app.get('/', (req, res) => {     
   res.send('Hello World, from express'); 
});
//Start the server listening on our port
app.listen(port, () => console.log(`Starting the server listening on port ${port}!`))

Start the server:

ole@mkt:~/Temp/api$ node hello-api.js 
Starting the server listening on port 3000!

Start your browser and visit http://localhost:3000/ . You should see:

Hello World, from express

Now lets create our greeting endpoint.

First we need to install some middle ware so that express can decode the body of our http request:

npm i body-parser

Then import and configure the body-parser :

//Add this statement to the top of hello-api.js
const bodyParser = require('body-parser');

Configure the body parser:

//Add this below the port configuration
app.use(bodyParser.urlencoded({ extended: false }));

After this is done, start the app again and make sure it works:

ole@mkt:~/Temp/api$ node hello-api.js

It should log the normal startup message.

Now lets test grabbing the url parameters :name

// Test getting the name
app.get("/api/hello/:name", function (req, res) {
    res.send("Name; " + req.params.name);
});

Start the server and try this request:

http://localhost:3000/api/hello/fireflysemantics

The browser should show:

Name: fireflysemantics

Lets capitalize the name:

// Test the capitalized  name
app.get("/api/hello/:name", function (req, res) {
    let name = req.params.name
    let capitalizedName = 
         name.charAt(0).toUpperCase() + 
         name.slice(1)
   res.send("Name: " + capitalizedName);
});

Restart server and visit:

http://localhost:3000/api/hello/fireflysemantics

The browser should show:

Name: Fireflysemantics

Finally return the JSON greeting object. Notice that we are using res.json instead of res.send :

// Test the greeting response
app.get("/api/hello/:name", function (req, res) {
let name = req.params.name
let capitalizedName = name.charAt(0).toUpperCase() + name.slice(1)
res.json(
    {
        name: name,
        greeting: `Hello there ${capitalizedName}, it's nice to meet you!`
    })
})

Restart the server and test the request:

http://localhost:3000/api/hello/fireflysemantics

The browser should show:

{"name":"fireflysemantics","greeting":"Hello there Fireflysemantics, it's nice to meet you!"}

Here’s the full source:

Related Concepts

Capitalizing the First String Letter in Javascript

Brought to You By

Firefly Semantics Supply Chain and Big Data Analytics for the Cloud