function removeDuplicatesAndCalculateDifference(array1, array2) {
  // 去重
  var result = [];
  var setA = new Set();

  for (var i = 0; i < array1.length; i++) {
    if (!setA.has(array1[i])) {
      result.push(array1[i]);
      setA.add(array1[i]);
    }
  }

  // 计算差异
  var setB = new Set(array2);
  var difference = [];

  for (var i = 0; i < result.length; i++) {
    if (!setB.has(result[i])) {
      difference.push(result[i]);
    }
  }

  return difference;
}

// 示例用法
var array1 = [1, 2, 3, 4, 5, 5, 6];
var array2 = [4, 5, 6, 7, 8];
var difference = removeDuplicatesAndCalculateDifference(array1, array2);

console.log(difference); // 输出 [1, 2, 3]