## Introduction.

Express.js is a back end web application framework that is used to build restful APIs with Node js . It is designed for building web applications and APIs. It is a standard server framework for Node js. It is a small framework that works on top of Node.js web server functionality to simplify its APIs and add helpful new features.

## Prerequisite. -

Download any code editor e.g. VS code. Visual Studio code which is a code editor with support for development operations like debugging, task running, and version control. Go to https://code.visualstudio.com

![vs code installation](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/gy7sis1llecx297gioh0.png) - Download and install the Node.js application, which is the environment in which express.js will run. Got to https://node.js.org ![Nodejs installation](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/tyb07gekj9mo4stu7goc.png) ### STEP 1: Create a folder in a terminal. Once Node.js is installed NPM(Node Package Manager) is also installed. Create a Folder in the terminal. ``` mkdir express_js ``` ``` cd express_js ``` ### STEP 2: Create a file We need to create a file and name it app.js. ``` touch app.js ``` ### STEP 3: Install the NPM. Now, we install the Npm (Node Package Manager) in the terminal using the command below; ``` npm init -y ``` _PS: The image below explains the folder creation, file creation, installation of npm(node package manager)._ ![folder creation, file creation and installation of npm](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/vj9almk4m6f29wkm5twu.png) ``` "code ." (This command is used to open the folder in your coding environment). ``` _**NOTE:** The “npm init” command will initialize a project and create the package.json file._ ### STEP 4: Install Express.js, Nodemon and Morgan In other to use express.js in the file, express.js has been pre-installed while installing the node.js. To install Express.js use the command below in the terminal. ``` npm install express ``` The nodemon npm Module is a module that develop node.js based applications by automatically restarting the node application when file changes in the directory are detected. Nodemon is a Dev Dependency module. Installing Nodemon is similar to installing express.js, Nodemon has been pre-installed while installing the node.js. To install Nodemon us the command below in the terminal. ``` npm install nodemon --save-dev ``` Morgan is another HTTP request logger middleware for Node. js. It simplifies the process of logging requests to your application. Also, the morgan dependency has been pre-installed while installing node.js. To install Morgan use the command below in the terminal. ``` npm install morgan ``` ### STEP 5: Import Express.js Import the express file that was created in the package.json file into the app.js file using the JavaScript code below; ```javascript const express = require("express"); ``` ### STEP 6: Make an Express.js Function The function defines the express as a function. ```javascript const app = express (); ``` ### STEP 7: Create a Route The route helps to determine how an application responds to a client request to a particular endpoint, which is a URL (or path) and a specific HTTP request method (GET, POST, and so on). Here, we want to send a message to the server "Hello World" ```javascript app.get( "/", (req,res) => { res.send("Hello world") }) ``` _**NOTE:** req means request, while res means response._ ### STEP 8: Create a Port Number The creation of port number helps to specify the port on which we want our app to listen. The port number ranges from 0 - 65000. Now create a port number of your choice, but for this sake of this we will be using "3030" ```javascript const port = 3030; ``` ### STEP 9: Listen to your server Listening refers to the process where a server waits for incoming connections from clients. ```javascript app.listen(port, ()=>{ console.log (`server is running on http:localhost:${port}`); }); ``` ``` **NOTE:** The local host = "127.0.0.1" ``` ![javascript](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/n7a7f4a9pv5yhslhnpin.png) ### STEP 10: Run the code in your terminal. Using the commands below you can run the code in your terminal. ``` node app.js ``` ![npm app.js](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/fqbcuanmjj1tigetbg3x.png) or ``` npm start ``` ![npm start](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/ka44nngvdbb2pyb3sayw.png) _**NOTE:** “npm start” is a run command from your scripts located in your package.json file._ ``` npm run dev ``` ![npm run dev](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/oe0mltw79lh8qxlukv60.png) _**NOTE:** "npm run dev" is used to execute specific scripts defined in the package. JSON file, particularly those scripts related to the development environment setup._ ### STEP 11: Launch the link in the browser. Using the link that was generated launch it on any browser e.g. goggle chrome, mozilla fire fox, opera, safari etc.. ``` http://localhost:3030 ``` ![Hello World](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/8k9ck1f2u3lcagqdhysb.png)

marvie_shoyoye

Create a simple Server using Express.js.

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