Answer

The some() method returns true as soon as at least one existing array element satisfies the callback condition. If no element matches, it returns false.

Array.prototype.mySome = function (callback, thisArg) {
  if (this == null) {
    throw new TypeError("Array.prototype.mySome called on null or undefined");
  }

  if (typeof callback !== "function") {
    throw new TypeError("Callback must be a function");
  }

  const array = Object(this);
  const length = array.length >>> 0;

  for (let i = 0; i < length; i++) {
    if (i in array && callback.call(thisArg, array[i], i, array)) {
      return true;
    }
  }

  return false;
};

console.log([1, 3, 5, 8].mySome(n => n % 2 === 0));
// true

Explanation

The method short-circuits on the first matching element. It returns false for an empty array because no element satisfies the condition.