Answer

The forEach() method executes a callback for every existing element in an array. It returns undefined and does not build a result array.

Array.prototype.myForEach = function (callback, thisArg) {
  if (this == null) {
    throw new TypeError("Array.prototype.myForEach 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);
    }
  }
};

const result = [10, 20, 30].myForEach((value, index) => {
  console.log(index, value);
});

console.log(result); // undefined

Explanation

• The callback executes for each existing index.
• The original array is not automatically modified, although the callback can modify it.
• forEach() cannot be stopped early with break or a callback return value.
• The iteration length is captured before the loop, matching native behavior more closely than repeatedly reading the length.