JavaScript - lesson 5 | HackIndia Skills

JavaScript - lesson 5 | HackIndia Skills | HackIndia

Example

Common project data

Imagine a simple student event planner. Your project may fetch this later. For now, practise on local data.

const events = [
  { id: 1, title: "AI Meetup", city: "Bengaluru", fee: 0, seats: 12 },
  { id: 2, title: "JS Workshop", city: "Pune", fee: 299, seats: 0 },
  { id: 3, title: "Design Jam", city: "Bengaluru", fee: 149, seats: 5 }
];

const eventCards = events.map((event) => ({
  id: event.id,
  label: `${event.title} - ₹${event.fee}`,
  available: event.seats > 0
}));

const freeEvents = events.filter((event) => event.fee === 0);

const puneEvent = events.find((event) => event.city === "Pune");

const hasSoldOutEvent = events.some((event) => event.seats === 0);

const totalSeats = events.reduce((sum, event) => sum + event.seats, 0);

console.log(eventCards);
console.log(freeEvents);
console.log(puneEvent);
console.log(hasSoldOutEvent);
console.log(totalSeats);

Common mistake

Do not mutate blindly

Methods like map and filter return new arrays. That is usually safer for project code because your original data stays unchanged.

sort changes the original array. If you need sorting, copy first.

const sortedByFee = [...events].sort((a, b) => a.fee - b.fee);

console.log(sortedByFee);
console.log(events); // original order is still safe

Tip

Name the callback

A good callback name makes your code read like English. This is better than writing short names everywhere.

If AI gives you code with x, y, item1, or data2, rename them before you commit.

const bengaluruEvents = events.filter((event) => event.city === "Bengaluru");

const titles = bengaluruEvents.map((event) => event.title);

Array Methods That Matter

Choose by result

Why this matters

Pick the method

Common project data

Do not mutate blindly

Name the callback

Check AI output

Do this now

Quick check