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# Web Engineering

**DHBW Stuttgart** · Informatik / Wirtschaftsinformatik

**Sommersemester 2026** · Sitzung 4 — Node.js: Scripting, Running and Building

---

# Inhalt

1. Node.js: was und warum
2. `node --check`, `node -e` (One-Liner)
3. Module: `require` / `import`, `__dirname` / `__filename`
4. HTTP-Server (built-in)
5. `fs` — Dateien lesen / schreiben
6. `package.json` — Aufbau und Lifecycle
7. npm Scripts
8. Module exportieren

---

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# Node.js – Scripting, Running and Building

---

# Node.js – Was ist das?

- JavaScript Runtime (V8 Engine)
- Server-side JavaScript
- npm Package Manager
- Ideal für: APIs, CLI Tools, Automation

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![bg fit](./assets/demos/nodejs-usecases.png)


---

# node --check und node -e

```bash
# Syntax check only
node --check script.js

# One-liner
node -e "console.log('Hallo Welt')"
```

---

# node -e Beispiele

```bash
# String
node -e "console.log('Hello ' + process.argv[2])" Welt

# File reading (ESM via --input-type)
node --input-type=module -e \
  "import { readFileSync } from 'node:fs'; \
   console.log(readFileSync('data.json', 'utf8'))"

# JSON parsen
node -e "console.log(JSON.parse(process.argv[1]))" '{"a":1}'
```

---

# Module laden – ESM (modern)

`"type": "module"` in `package.json` einschalten.

```javascript
// Eigene Datei (Endung .js erforderlich!)
import { add, greet } from "./utils.js";

// npm Modul (default + named import)
import express from "express";
import { Router } from "express";

// Built-in (mit "node:"-Präfix)
import { readFileSync } from "node:fs";
import { join } from "node:path";
```

<small>**Legacy CJS:** `const express = require("express")` — funktioniert noch, aber ESM ist heute Standard.</small>

---

# Pfad-Auflösung in ESM

```javascript
import { fileURLToPath } from "node:url";
import { dirname, join } from "node:path";

const __filename = fileURLToPath(import.meta.url);
const __dirname  = dirname(__filename);

const configPath = join(__dirname, "..", "config.json");
```

<small>In ESM gibt es **kein** automatisches `__dirname` / `__filename` (anders als CJS). Über `import.meta.url` rekonstruieren.</small>

---

# HTTP Server mit Node.js (Built-in)

**ESM** (modern, `"type": "module"` in `package.json`):
```javascript
import { createServer } from "node:http";

const server = createServer((req, res) => {
  res.writeHead(200, { "Content-Type": "text/html" });
  res.end("<h1>Hallo Welt!</h1>");
});

server.listen(3000, () => {
  console.log("Server läuft auf Port 3000");
});
```

<small>**CommonJS** (legacy): `const http = require("http");` — funktioniert noch, aber neue Projekte nutzen ESM.</small>

---

# fs – Dateien lesen/schreiben

```javascript
import { readFile, readFileSync, writeFile } from "node:fs";
import { readFile as readFileAsync } from "node:fs/promises";

// Promise-API (empfohlen, modern)
const data = await readFileAsync("data.json", "utf8");
console.log(JSON.parse(data));

// Callback-API
readFile("data.json", "utf8", (err, data) => {
  if (err) throw err;
  console.log(JSON.parse(data));
});

// Sync (nur für Setup / Scripts)
const content = readFileSync("data.json", "utf8");
```

---

# package.json – Das Herzstück

```json
{
  "name": "mein-projekt",
  "version": "1.0.0",
  "main": "index.js",
  "scripts": {
    "start": "node index.js",
    "dev": "node --watch index.js",
    "test": "node --test"
  },
  "dependencies": {
    "express": "^4.18.0"
  },
  "devDependencies": {
    "nodemon": "^3.0.0"
  }
}
```

---

# npm Scripts

```bash
# npm run <script>
npm run start
npm run dev

# Mit Argumenten
npm run build -- --production

# Lifecycle scripts
npm install  → postinstall
npm start    → start (direkt)
```

---

# Node.js Module – exports (ESM)

```javascript
// utils.js — named exports
export const add = (a, b) => a + b;
export const greet = (name) => `Hallo ${name}!`;

// utils.js — default export
export default {
  add,
  greet
};
```

```javascript
// nutzen
import { add, greet } from "./utils.js";       // named
import utils from "./utils.js";                // default
import utils, { add } from "./utils.js";       // beides
```

<small>**Legacy CJS:** `module.exports = { add, greet }` + `const { add } = require("./utils")`.</small>