Arrays

Arrays are one of the most important data structures in JavaScript. They allow you to store multiple values in a single variable.

1. What are Arrays? 📦

What is it? An ordered list of values. Each value is called an "element" and has a numeric position called an "index".

Why use it? To store lists of data (e.g., a shopping list, user IDs, or colors) without creating separate variables for each item.

How it works: Arrays are zero-indexed, meaning the first item is at index 0.

2. Basic Methods (Add/Remove) ➕➖

JavaScript provides built-in methods to add or remove items easily.

• push(): Add to end
• pop(): Remove from end
• unshift(): Add to start
• shift(): Remove from start

3. Iterating Arrays 🔄

How do you go through every item in an array?

forEach (Execute code for each item)

Great for side effects (printing, saving to DB).

map (Transform items)

Creates a new array by changing each item.

filter (Select items)

Creates a new array with only items that pass a test.

4. The reduce Method 💪

What is it? The most powerful array method. It takes an array and "reduces" it to a single value (e.g., a sum, an object, or a number).

How it works: It loops through the array, maintaining an "accumulator" (running total).

5. Searching & Sorting 🔍

• find(): Returns the first item that matches.
• includes(): Returns true if item exists.
• sort(): Sorts the array (converts to string by default!).

Practical Example: Shopping Cart 🛒

Quiz

Key Takeaways

✅ Arrays are ordered lists (0-indexed).
✅ push/pop add/remove from end.
✅ map transforms, filter selects.
✅ reduce combines everything into one value.
✅ sort needs a compare function for numbers.

What's Next?

Arrays are powerful, but modern JavaScript gives us even better tools. Next, we'll learn Spread, Rest, and Destructuring!

Keep coding! 🚀