✅ Array.isArray() Polyfill

The Array.isArray() method determines whether the passed value is an Array.

✅ Implementation

function customIsArray(value) {
    // Return false if the value is null or undefined
    if (value === null || value === undefined) {
        return false;
    }

    // Use Object.prototype.toString to reliably check the type of value
    // This method returns '[object Array]' for arrays
    return Object.prototype.toString.call(value) === '[object Array]';
}

Explanation:

1. Null and Undefined Check : The function first checks if value is null or undefined. If it is, it immediately returns false.
2. Reliable Type Checking : For all other values, the function uses Object.prototype.toString.call(value). This method returns a string in the format "[object Type]", where Type is the internal class of the object. For arrays, it returns "[object Array]".
3. Why This Works : Object.prototype.toString is a reliable way to determine the internal class of an object, which helps accurately identify arrays. This is a cross-environment solution that works similarly to Array.isArray().

Behavior:

• Returns true for arrays : Works for empty arrays, populated arrays, arrays created with the Array constructor, and even Array.prototype.
• Returns false for non-arrays : Includes undefined, null, objects, numbers, strings, booleans, and array-like objects such as TypedArrays.