在一个数组中搜索多个值的代码是如何工作的?

function find_duplicate_in_array(arra1) {

  // Temporary count of each item in the input array/
  var object = {};
  // Final result containing each item that has been seen more than one time.
  var result = [];

  // For each item of the array...
  arra1.forEach(function (item) {
    // If it is not in the temporary object, initialize it to 0.
    if(!object[item])
      object[item] = 0;
    // Add one since we just have found it!  
    object[item] += 1;
  })


  // Now, every item of the input array has been counted in object.
  // For each item of object:
  for (var prop in object) {
    // If it has been counted more than one time, add it to the result.
    if(object[prop] >= 2) {
      result.push(prop);
    }
  }

  // Return the result.
  return result;

}

console.log(find_duplicate_in_array([1, 2, -2, 4, 5, 4, 7, 8, 7, 7, 71, 3, 6]));