🧠 HW 3 — Intro to TypeScript

Welcome to your second assignment in Full-Stack Development!
You’ll take what you learned from JavaScript and now write safer, cleaner, and more reliable code with TypeScript.

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⚙️ Setup

Make sure you have Node.js (v18 or newer) and TypeScript installed.

Check your Node version:

node -v

Install TypeScript globally (only once):

npm install -g typescript

To compile a TypeScript file:

tsc Problem1.ts

Run the compiled JavaScript file:

node Problem1.js

Or, if you prefer one command:

npx ts-node Problem1.ts

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📁 Folder Structure

typescript-assignment-2/
├── Problem1.ts
├── Problem2.ts
├── Problem3.ts
├── Problem4.ts
├── Problem5.ts
└── Problem6.ts

Each problem file is stand-alone — no imports, no exports, no frameworks. Open them in VS Code, write your solution inside the given function, and test using the console.log examples.

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📚 Problems Overview

🧩 Problem 1 – concatNumbers

Write a function that takes two numbers, converts them to strings, and concatenates them.

concatNumbers(4, 5);   // "45"
concatNumbers(5, -9);  // "5-9"

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🧩 Problem 2 – arrayOfStudents

Given two arrays (names and ages), return an array of student objects.

[
  { name: "Joe", age: 50 },
  { name: "Schmo", age: 60 }
]

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🧩 Problem 3 – studentsTaughtByProf

Given a Professor object containing classes and students, return all unique student names sorted by age (ascending).

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🧩 Problem 4 – allAthletes

Given an array of Student or Athlete objects, return a new array where all become Athletes. Existing athletes keep their original sport; new ones get the default sport you provide.

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🧩 Problem 5 – countOccurrences

Write a generic function that counts how many times a value appears in an array.

countOccurrences([2, 4, 6, 6, 8], 6);  // 2
countOccurrences([true, true, true], false);  // 0

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🧩 Problem 6 – verifyUser

Given a possibly incomplete user object, return either:

• the user itself (if all properties exist), or
• an array of missing property names.

Also handle null or undefined safely.

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🧪 Testing

Every file already includes small example tests at the bottom like:

console.log(concatNumbers(4, 5));

Run each one manually:

npx ts-node Problem1.ts

No external testing libraries needed.

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💡 Tips

• Always give explicit parameter and return types.
• Use type aliases to define object shapes.
• Use ? for optional properties.
• Use union (|) and intersection (&) types when combining data.
• Experiment with type narrowing using typeof.

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✅ Learning Goals

By completing this assignment, you should be able to:

✔️ Understand how TypeScript checks types at compile-time ✔️ Define and reuse custom types ✔️ Work safely with optional data ✔️ Create generic and reusable functions ✔️ Write JavaScript code that’s more predictable and self-documenting

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🏁 Submission

When finished, push your completed .ts files to your GitHub Classroom repository. Ensure all files compile cleanly (no red squiggles or compiler errors) before submitting.