collection.at(index) - Get Item at Specific Index

Quick Start (30 seconds)

const items = createCollection(['apple', 'banana', 'orange', 'grape']);

// Get by index
const first = items.at(0);
console.log(first);  // "apple"

const second = items.at(1);
console.log(second);  // "banana"

// Negative indices (from end)
const last = items.at(-1);
console.log(last);  // "grape"

const secondLast = items.at(-2);
console.log(secondLast);  // "orange"

// Out of bounds returns undefined
const outOfBounds = items.at(10);
console.log(outOfBounds);  // undefined ✨

What just happened? You accessed items by position with support for negative indices!

What is collection.at(index)?

at(index) returns the item at the specified index, with support for negative indices.

Simply put: it gets an item by its position, counting from start (positive) or end (negative).

Think of it as picking a book from a shelf - you can count from the left or from the right.

Syntax

collection.at(index)

Parameters:

• index (number) - Position of item
  • Positive: from start (0-based)
  • Negative: from end (-1 = last)

Returns:

• Item at index
• undefined if out of bounds

Why Does This Exist?

The Problem:

// Direct array access breaks abstraction
const last = collection.items[collection.items.length - 1];

The Solution:

// Clean collection API with negative index
const last = collection.at(-1);

Basic Usage

const colors = createCollection(['red', 'green', 'blue']);

colors.at(0);   // "red"
colors.at(1);   // "green"
colors.at(2);   // "blue"
colors.at(-1);  // "blue" (last)
colors.at(-2);  // "green" (second from end)
colors.at(10);  // undefined

Real-World Examples

Example 1: Get First and Last

const scores = createCollection([85, 92, 78, 95, 88]);

console.log('First score:', scores.at(0));   // 85
console.log('Last score:', scores.at(-1));   // 88
console.log('Average:', (scores.at(0) + scores.at(-1)) / 2);

Example 2: Access Recent Items

const logs = createCollection([...activityLogs]);

// Get 3 most recent logs
const recent = [
  logs.at(-1),
  logs.at(-2),
  logs.at(-3)
].filter(Boolean);

recent.forEach(log => console.log(log.message));

Example 3: Pagination

const items = createCollection([...products]);
const pageSize = 10;

function getPage(pageNum) {
  const start = pageNum * pageSize;
  const page = [];
  
  for (let i = 0; i < pageSize; i++) {
    const item = items.at(start + i);
    if (item) page.push(item);
  }
  
  return page;
}

Important Notes

1. Negative Indices Count from End

const items = createCollection([1, 2, 3, 4, 5]);

items.at(-1);  // 5 (last)
items.at(-2);  // 4 (second from end)
items.at(-5);  // 1 (first)

2. Returns undefined for Out of Bounds

const items = createCollection([1, 2, 3]);

items.at(10);   // undefined
items.at(-10);  // undefined

3. Use length Property for Bounds

const lastIndex = collection.length - 1;
const last = collection.at(lastIndex);

When to Use

Use at() For: ✅ Access by index
✅ Get first/last items
✅ Negative indices

Don't Use For: ❌ Search by value - Use find()
❌ Get index - Use indexOf()

Summary

What is at(index)?
Returns item at index with negative index support.

Remember: Negative indices count from end, returns undefined if out of bounds! 🎉