What is localhost 3000?

I am new to web development. When I read how to setup react project I see localhost:3000. I searched for it but any of the answers didn't answer what localhost:3000 mean.

5 Answers

To make you understand this you should understand that you need a web server to host the application to run on the web. Then it will be available for most of the people.

But that application needs to be developed somewhere. In this case you need a local server. There are several local server instances like IIS, Wamp, Xampp and nodejs.

If you are getting started with react then you most probably using react app development with its cli creat-react-app or in short CRA. With this structure and configuration of this app, it is hosted locally in node server and on port 3000.

So, to answer your question. localhost is the address which denotes to 0.0.0.0 or 127.0.0 and it chose the port 3000 you can configure it to other ports too.

So, when you type in the addressbar of the browser you can see the first page hosted from your app. You can make use of etc/hosts file to a local name just like to too.

Localhost:3000 is the URL adress at which your web app (during development) is accessible if you started it (with a command in the console, like for example: npm start). Localhost means that it's your computer that is hosting the app, and it doesn't mean that it's accessible on other computers. 3000 is the port at which your web app is accessible, and it can be changed to any 4 digit number from 1000 to 9999 I believe. It's made like that so you can host multiple apps at the same time if you want, at different ports of course. Most production environments have the port set to 3000 by default.

localhost 3000 is the default port that runs on your computer for react app. you can change it anytime in the package.json

So as analogy think your computer as home and ports are room numbers that you have at home.

So your react app is living at 3000. room when you run npm start

Lets pretend you're 5 years old again. You have a play date coming up with Suzy from summer camp. You're very excited.

You just learned to play String Telephone in science class and you would like to impress Suzy by playing it with her.

You gather up the materials (two cups, string) and affix the string to the cups. You want to test the game to ensure it works when Suzy arrives. You can talk into one cup and put the other cup up to your ear, but in order for it to work, the string must be taut.

You hold your finger out and pull the string around it to keep it taut.

Now you're able to confirm that your brain thought of something to say (Application Layer) and your muscles moved to create sound waves (Presentation Layer) that hit the bottom of the cup which then move the string (Transport Layer).

Your finger is localhost.