✅ Array.prototype.every() Polyfill

The every() method tests whether all elements in the array pass the test implemented by the provided function.

✅ Implementation

Array.prototype.customEvery = function (callback, thisArg) {
    if (typeof callback !== 'function') {
        throw new TypeError(callback + ' is not a function');
    }

    for (let i = 0; i < this.length; i++) {
        if (!callback.call(thisArg, this[i], i, this)) {
            return false; // Return false immediately if one element fails
        }
    }

    return true; // Return true if all elements pass the test
};

// Example usage:
const input = [2, 4, 6, 8];
const isEven = (element) => element % 2 === 0;

console.log(input.customEvery(isEven)); // Output: true
console.log([2, 4, 5, 8].customEvery(isEven)); // Output: false
console.log([].customEvery(isEven)); // Output: true (empty array always returns true)

How It Works

1. Checks if callback is a function
   • If not, throws a TypeError (same behavior as Array.prototype.every).
2. Iterates through the array
   • Calls callback for each element with (element, index, array).
   • Uses .call(thisArg, ...) to bind thisArg if provided.
3. Returns early if any test fails
   • If callback returns false for any element, customEvery immediately returns false (optimized).
4. Returns true if all tests pass
   • If all elements satisfy the condition, it returns true.

Edge Cases Handled

✔ Empty array always returns true

✔ Stops checking as soon as one element fails (Optimized)

✔ Works with thisArg binding

✔ Throws an error if callback is not a function

This implementation is efficient, clean, and mirrors Array.prototype.every exactly.