➡️ Array.prototype.unshift() Polyfill

The unshift() method adds one or more elements to the beginning of an array and returns the new length.

✅ Implementation

Array.prototype.customUnshift = function (...elements) {
    // Move existing elements to the right to make space for new elements
    for (let i = this.length - 1; i >= 0; i--) {
        this[i + elements.length] = this[i];
    }

    // Insert new elements at the beginning
    for (let i = 0; i < elements.length; i++) {
        this[i] = elements[i];
    }

    return this.length; // Return new array length
};

// Example usage:
const array = [1, 2, 3];
array.customUnshift(4, 5);

console.log(array); // Output: [4, 5, 1, 2, 3]
console.log(array.customUnshift(0)); // Output: 6 (new length of array)
console.log(array); // Output: [0, 4, 5, 1, 2, 3]

How It Works

1. Shifts existing elements to the right
   • Loops backward to prevent overwriting elements.
   • Moves each element to a new position based on the number of elements being added.
2. Inserts new elements at the beginning
   • Loops forward to place new elements in their correct positions.
3. Returns the new array length
   • Mimics unshift() behavior by returning the updated length.

Edge Cases Handled

✔ Works with multiple elements: customUnshift(4, 5, 6)

✔ Works with empty arrays: [].customUnshift(1, 2, 3)

✔ Works with no arguments: array.customUnshift() (returns unchanged length)

✔ Preserves element order correctly

This implementation is efficient and follows the exact behavior of Array.prototype.unshift.