JavaScript Async & OOP Lab

Master Object-Oriented Programming and asynchronous JavaScript through 12 desi, story-based challenges! From Ramu ka samosa cart to a full startup incubator system, each problem puts you in a real Indian scenario where you need to use this, classes, inheritance, Promises, async/await, and more.

Total: 100 points across 12 challenges

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Prerequisites

• Node.js v20 or higher
• Git
• A code editor (VS Code recommended)

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Getting Started

1. Accept the assignment

Click the GitHub Classroom invitation link shared by your instructor. This will create a personal copy of this repository under your GitHub account.

2. Clone your repository

git clone <your-repo-url>
cd js-async-oop-lab

Replace <your-repo-url> with the URL from your GitHub Classroom repo (the green Code button).

3. Install dependencies

npm install

4. Verify everything works

npm test

You should see all tests failing — that's expected! Your job is to make them pass.

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How to Solve the Challenges

Step 1 — Open a challenge file

All challenges live in the src/ folder. Start with src/01-samosa-wala.js and work your way up.

src/
├── 01-samosa-wala.js            ← Start here
├── 02-lassi-stand.js
├── 03-dabba-delivery.js
├── 04-cricket-academy.js
├── 05-haveli-mansion.js
├── 06-chai-promise.js
├── 07-zomato-delivery.js
├── 08-irctc-booking.js
├── 09-swiggy-batch.js
├── 10-paytm-retry.js
├── 11-temple-queue.js
└── 12-startup-incubator.js

Step 2 — Read the story and rules

Each file has a detailed JSDoc comment at the top that explains:

• The kahani (story — a real Indian scenario)
• The rules your function/class must follow
• The parameters and return values

Read it carefully — every edge case and requirement is described there.

Step 3 — Write your solution

Replace // Your code here with your implementation:

// Before
export function createSamosaCart(ownerName, location) {
  // Your code here
}

// After (example)
export function createSamosaCart(ownerName, location) {
  return {
    owner: ownerName,
    location,
    menu: { samosa: 15, jalebi: 20, kachori: 25 },
    sales: [],
    sellItem(itemName, quantity) {
      if (!this.menu[itemName] || quantity <= 0) return -1;
      const total = this.menu[itemName] * quantity;
      this.sales.push({ item: itemName, quantity, total });
      return total;
    },
    // ... more methods
  };
}

Step 4 — Run the test for that challenge

npm test -- 01-samosa

You can use any part of the filename to match:

npm test -- 02-lassi
npm test -- 03-dabba
npm test -- cricket
npm test -- haveli
npm test -- chai-promise

Step 5 — Fix and repeat

If tests fail, read the error messages — they tell you exactly what was expected vs. what your function returned. Fix your code and run the test again.

Step 6 — Move to the next challenge

Once all tests pass for a challenge, move on to the next one. They get progressively harder.

Run all tests at once

npm test

Watch mode (auto re-run on save)

npm run test:watch

This re-runs tests every time you save a file — very handy while working.

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Challenges

#	File	Kahani	Concept	Points
01	01-samosa-wala.js	Ramu ka Samosa Cart	this keyword basics	7
02	02-lassi-stand.js	Punjab ki Lassi Stand	Constructor functions & prototype	7
03	03-dabba-delivery.js	Mumbai Dabba Delivery	ES6 Classes	8
04	04-cricket-academy.js	Cricket Academy	Inheritance (extends, super)	8
05	05-haveli-mansion.js	Purani Haveli Security	Encapsulation (private fields #)	8
06	06-chai-promise.js	Tapri ki Chai Promise	Promise creation (resolve/reject)	9
07	07-zomato-delivery.js	Zomato Delivery Pipeline	Promise chaining (.then/.catch)	9
08	08-irctc-booking.js	IRCTC Train Booking	async/await	9
09	09-swiggy-batch.js	Swiggy Batch Delivery	Promise.all, .race, .allSettled	9
10	10-paytm-retry.js	Paytm Payment Retry	Error handling & custom errors	9
11	11-temple-queue.js	Temple Darshan Queue	Static methods, getters, Symbol.iterator	9
12	12-startup-incubator.js	Startup Incubator	Capstone: OOP + async + this	9

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Submitting Your Work

1. Check your progress

Run all tests to see how many you've solved:

npm test

2. Stage your changes

git add src/

Important: Only add files from src/. Do not modify or commit test files.

3. Commit your work

git commit -m "Complete async-oop lab"

You can commit as many times as you want — each push triggers a new grading run.

4. Push to GitHub

git push origin main

5. Check your grade

After pushing, go to your repository on GitHub:

1. Click the Actions tab
2. You'll see a workflow run in progress (or completed)
3. Click on it to see which tests passed and your total score out of 100

You can push again to improve your score — GitHub Classroom will always use the latest result.

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Windows Users

If you are on Windows and npm test fails, use the Windows-specific scripts instead:

npm run test:win

For watch mode on Windows:

npm run test:win:watch

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Tips for Success

• JSDoc dhyan se padho — every rule and edge case is described there
• this samjho — understand how this behaves in regular functions vs arrow functions vs methods
• Inheritance chain samjho — super() call mandatory hai before using this in constructor
• Private fields (#) — these are truly private, not accessible from outside the class
• Promises — always return a Promise or use async/await, never forget error handling
• async/await — await only works inside async functions
• Don't modify the test files — only edit files in src/
• Commit often — don't wait until you've solved everything to push
• Use console.log() — add temporary logs to debug, then remove them before submitting

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Concepts Covered

• The this keyword and context binding (bind, call, apply)
• Constructor functions and the new keyword
• Prototypes and prototype-based inheritance
• ES6 Classes (class, constructor, methods)
• Inheritance with extends and super
• Encapsulation with private fields (#)
• Promise creation with new Promise(resolve, reject)
• Promise chaining with .then() and .catch()
• async/await for cleaner asynchronous code
• Promise.all, Promise.race, Promise.allSettled
• Custom error classes extending Error
• Retry patterns and error recovery
• Static methods and factory patterns
• Getters and setters
• Symbol.iterator for custom iterables
• Combining all OOP and async concepts together

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Troubleshooting

Problem	Solution
npm test shows "command not found"	Run npm install first
All tests fail with undefined	You haven't written your solution yet — that's expected
Tests say "expected X but received Y"	Your logic is close but not matching the rules — re-read the JSDoc
git push is rejected	Run git pull origin main first, then push again
Tests pass locally but fail on GitHub	Make sure you pushed all your changes (git status to check)
npm test fails on Windows	Use npm run test:win instead
Promise tests timeout	Make sure your promises resolve/reject — don't leave them hanging

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Good luck! Aur haan, classes aur promises likhte likhte chai peena mat bhoolna!