🎯 Array.prototype.at() Polyfill

The at() method takes an integer and returns the item at that index, allowing for positive and negative integers.

✅ Implementation

Array.prototype.customAt = function(index) {
    // Adjust negative index to count from the end of the array
    if (index < 0) {
        index += this.length; // Convert negative index to a positive one
    }

    // Return the element at the adjusted index, or undefined if out of bounds
    return index >= 0 && index < this.length ? this[index] : undefined;
};

// Example usage:
const array = [5, 12, 8, 130, 44];

console.log(array.customAt(2));   // Output: 8
console.log(array.customAt(-1));  // Output: 44
console.log(array.customAt(100)); // Output: undefined

Explanation:

• Negative index handling :

  If the index is negative, it’s adjusted by adding the array’s length. This makes -1 refer to the last element, -2 to the second-to-last, and so on.

• Bounds check :

  After adjusting the index, the function checks if it’s within the valid range (i.e., 0 <= index < this.length). If it’s valid, the element at that index is returned; otherwise, undefined is returned.

• Edge case :

  If the index is out of bounds (e.g., 100 for an array of length 5), it returns undefined.

Examples:

• customAt(2) returns the element at index 2 (which is 8).
• customAt(-1) returns the last element (44).
• customAt(100) returns undefined since the index is out of bounds.

This mimics Array.prototype.at while supporting both positive and negative indices.