adds recitation 3

Author: Aditya Shrivastava

docs/_data/schedule.yaml

@@ -191,7 +191,7 @@
     link: ''
     name: ''
   recitation:
-    handout: ''
+    handout: 'recitations/reci3-nodejs'
     name: 'Node Web Apps'
     quiz: ''
     slides: ''

docs/recitations/reci3-nodejs.md

@@ -0,0 +1,182 @@
+# Recitation #3
+### 17-356/17-766
+
+## What is Node.js
+- Open-source, cross-platform JavaScript runtime environment.
+- Event-driven architecture capable of asynchronous (non-blocking) I/O.
+- Suitable for fast, powerful, and scalable web applications.
+- JavaScript and Node.js are the most popular technologies for web development.
+
+## Npm (Node Package Manager)
+- Largest ecosystem of open-source libraries in the world.
+- npm registry - an online database of public and paid-for private packages.
+
+### How to find reliable, secure packages:
+1. Run `npm audit` after installing to check for vulnerabilities.
+2. Look for an active GitHub repository (stars, forks, and issues).
+3. Check `package.json` dependencies:
+    ```json
+    "dependencies": {
+      "axios": "^1.7.9",
+      "cra-template": "1.2.0",
+      "react": "^18.0.0",
+      "react-dom": "^18.0.0",
+      "react-scripts": "5.0.1",
+      "web-vitals": "^4.2.4"
+    }
+    ```
+
+## Simple Web Architecture
+- **Frontend**: React / Vue + RESTful APIs
+- **Backend**: Node.js
+- **Database**: PostgreSQL / MySQL / MongoDB
+
+## Node.js + MongoDB
+
+### What is MongoDB?
+- NoSQL document-based database.
+- Stores data in JSON-like BSON format.
+- Scalable, flexible, and schema-less.
+
+### Schema Example:
+```json
+{
+  "name": "Harry Potter",
+  "author": {
+    "name": "J.K. Rowling",
+    "followers": 789
+  },
+  "views": 123456
+}
+```
+
+### Node.js Asynchronous Execution
+```javascript
+function function1() {
+    setTimeout(() => {
+        console.log('function1');
+    }, 1000); // Delays execution by 1 second
+}
+function function2() {
+    console.log('function2');
+}
+function main() {
+    function1();
+    function2();
+}
+```
+
+### Output
+```
+function2
+function1
+```
+
+### Callback Functions
+
+1. Functions passed to another function
+2. Executes the callback after function1 completes
+
+Example
+```javascript
+function function1(callback) {
+    setTimeout(() => {
+        console.log('function1');
+        callback();
+    }, 1000);
+}
+function function2() {
+    console.log('function2');
+}
+function main() {
+    function1(function2);
+}
+```
+
+### Output
+```
+function1
+function2
+```
+
+### Promises and Promise Chains
+
+1. Structured callbacks that avoid "callback hell".
+2. Resolves the promise after function1 completes.
+
+Example
+```javascript
+function function1() {
+    return new Promise((resolve) => {
+        setTimeout(() => {
+            console.log('function1');
+            resolve();
+        }, 1000);
+    });
+}
+function function2() {
+    console.log('function2');
+}
+function main() {
+    function1().then(function2); // Waits for function1 before running function2
+}
+```
+
+Output
+```
+function1
+function2
+```
+
+### Generators
+1. Functions that can be exited/paused and later renamed
+
+Example
+```javascript
+function* main() {
+    yield new Promise((resolve) => {
+        setTimeout(() => {
+            console.log('function1');
+            resolve();
+        }, 1000);
+    });
+
+    console.log('function2');
+}
+const generator = main();
+generator.next().value.then(() => generator.next());
+```
+
+Output
+```
+function1
+function2
+```
+
+### Async/Await
+1. Combines generators and promises.
+2. Waits for function1 before running function2.
+3. Functions that use await must be declared as async.
+
+```javascript
+function function1() {
+    return new Promise((resolve) => {
+        setTimeout(() => {
+            console.log('function1');
+            resolve();
+        }, 1000);
+    });
+}
+function function2() {
+    console.log('function2');
+}
+async function main() {
+    await function1();
+    function2();
+}
+```
+
+```
+function1
+function2
+```