Express 101

Introduction

Express is HTTP framework for NodeJS and I think to practice using it by writing an application to find and replace a given string by another string. At the time of writing this sample, Express v5 is still under development, so we install it as follows:

npm install express@next

As always our project has configuration, so we need to have dotenv:

npm install dotenv

After that, we are going to have Typescript:

npm i -D typescript @types/express @types/node

npx tsc --init

For parsing request data based on content-type header we need the body-parser library:

npm install body-parser

npm i -D @types/body-parser

Up and Running

First you need to create .env as follows:

PORT=8080
TARGET="Foo"
REPLACED="Bar"

Then build:

npm run build

And, run the code:

npm start

We are ready to test it:

curl 127.0.0.1:8080/api/replace -H 'Content-Type: application/json' -d '{ "Hello": "Foo", "Bye": { "Name": "Foo", "Who": 1 } }'

Development

Running all above commands each time you change something takes time. So you can use the dev command as follows:

npm run dev

How it works?

We have an API named replaced that replaces a given string with another string in the request body. Request body is JSON structured, and we convert it into dictionary, so we can do the replacing process on values and don't change the keys.