firstrepeatingelement.js

function findFirstRepeatingElement(arr) {
  let count = {};
  for (let i = 0; i < arr.length; i++) {
    if (count[arr[i]]) {
      return arr[i];
    } else {
      count[arr[i]] = 1;
    }
  }
  return null;
}

// Example usage:
const arr = [2, 5, 1, 2, 3, 5, 1, 2, 4];
const firstRepeating = findFirstRepeatingElement(arr);
console.log(firstRepeating); // Output: 2