⬅️ Array.prototype.shift() Polyfill

The shift() method removes the first element from an array and returns that element.

✅ Implementation

Array.prototype.customShift = function () {
    if (this.length === 0) return undefined; // Return undefined if the array is empty

    const firstElement = this[0]; // Store the first element

    // Shift all elements to the left
    for (let i = 1; i < this.length; i++) {
        this[i - 1] = this[i];
    }

    this.length -= 1; // Reduce the length of the array

    return firstElement; // Return the removed element
};

// Example usage:
const array = [1, 2, 3];
const firstElement = array.customShift();

console.log(firstElement); // Output: 1
console.log(array);        // Output: [2, 3]
console.log([].customShift()); // Output: undefined (empty array case)

How It Works

1. Handles an empty array
   • If this.length === 0, it returns undefined, just like shift().
2. Stores the first element
   • Saves this[0] before modifying the array.
3. Shifts elements to the left
   • Iterates through the array and shifts elements to the left (this[i - 1] = this[i]).
4. Reduces the array length
   • this.length -= 1; effectively removes the last duplicate.
5. Returns the removed element
   • Mimics shift() behavior by returning the removed item.

Edge Cases Handled

✔ Works on normal arrays

✔ Works on empty arrays ([].customShift() → undefined)

✔ Modifies the original array in place

✔ Returns the first element as expected

This implementation is simple, efficient, and follows Array.prototype.shift exactly.