> For the complete documentation index, see [llms.txt](https://jianghua-yjhs-organization.gitbook.io/in-depth-understanding-of-node.js-core-ideas-and/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jianghua-yjhs-organization.gitbook.io/in-depth-understanding-of-node.js-core-ideas-and/chapter1-2.md).

# Starting with hello world

#### Starting with "Hello World"

Let's start with a piece of code that is familiar to everyone, <https://nodejs.org/en/about/>. Like learning any language, a simple "Hello World" program can give you an intuitive understanding of node.js.

```js
const http = require('http');
const hostname = '127.0.0.1';
const port = 1337;

http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('Hello World\n');
}).listen(port, hostname, () => {
  console.log(`Server running at http://${hostname}:${port}/`);
});
```

Let's take a look at how many core modules are involved in the first line of code, and start our journey of analyzing node.js source code.

The first line: `const http = require('http');` involves two modules, the module and http modules.

Main code

```js
http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('Hello World\n');
}).listen(port, hostname, () => {
  ...
});
```

* First, let's understand the inheritance relationship of the HTTP Server, which is helpful for a better understanding of the code.

![http](https://1480070255-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FpQej5YhPWrVsBjduy3EQ%2Fuploads%2Fgit-blob-a5a6f20115625e585ee7288d3441ffba2c657007%2F270064-edbf9b53812f0433.png?alt=media)

This also involves the event and net modules.

The last sentence:

```js
console.log(`Server running at http://${hostname}:${port}/`);
```

Here, the console module is used, but it is not obtained through `require`. This brings us to the global object, the top-level object of Node.js. I'll leave it as a teaser for now, and I'll explain it in detail in the global section later.

If you want to view some debugging logs of node, you can set the NODE\_DEBUG environment variable, for example:

```shell
NODE_DEBUG=HTTP,STREAM,MODULE,NET node http.js
```

View V8 logs

```shell
node --trace http.js
```

#### Summary

A simple hello world program involves multiple modules, but behind it is the wisdom of the Node community, a high-level abstraction of web services and asynchronous IO. As the saying goes, simplicity is the ultimate sophistication!

Let's start the journey of Node.js source code with a famous quote from Linus Torvalds.

> Talk is cheap, show me the code.