🔍 Array.prototype.includes() Polyfill

The includes() method determines whether an array includes a certain value, returning true or false.

✅ Implementation

Array.prototype.customIncludes = function (searchElement, fromIndex = 0) {
    if (fromIndex < 0) {
        fromIndex = Math.max(this.length + fromIndex, 0);
    }

    for (let i = fromIndex; i < this.length; i++) {
        if (this[i] === searchElement || (Number.isNaN(this[i]) && Number.isNaN(searchElement))) {
            return true;
        }
    }

    return false;
};

// Example usage:
const array = [1, 2, 3];

console.log(array.customIncludes(2)); // Output: true
console.log(array.customIncludes(4)); // Output: false
console.log(array.customIncludes(3, -1)); // Output: true
console.log(array.customIncludes(1, -3)); // Output: true
console.log([NaN].customIncludes(NaN)); // Output: true

How It Works:

1. Parameters :
   • searchElement: The element to search for in the array.
   • fromIndex: The index to start the search from (defaults to 0). Negative values are adjusted to count from the end of the array.
2. Iteration : The customIncludes method iterates through the array starting from fromIndex.
3. Comparison : For each element, it checks if the element is strictly equal (===) to searchElement or if both are NaN.
4. Return Value :
   • Returns true if searchElement is found.
   • Returns false if searchElement is not found.

Example:

• customIncludes(2) returns true because 2 is in the array.
• customIncludes(4) returns false because 4 is not in the array.
• customIncludes(3, -1) returns true because 3 is found when counting from the end.
• customIncludes(1, -3) returns true because 1 is found when counting from the end.
• [NaN].customIncludes(NaN) returns true because NaN is found in the array.

Key Features:

• Supports negative fromIndex by adjusting it to count from the end of the array.
• Iterates through the array and checks for strict equality (===) with searchElement or if both are NaN.
• Returns a boolean indicating whether searchElement is found in the array.