从多维数组中提取列的子数组，并修改原始数组以删除这些列JavaScript

function extractColumns(arr, columns) {
  var result = [];
  for (var i = 0; i < arr.length; i++) {
    var row = [];
    for (var j = 0; j < columns.length; j++) {
      row.push(arr[i][columns[j]]);
    }
    result.push(row);
  }
  return result;
}

function removeColumns(arr, columns) {
  for (var i = 0; i < arr.length; i++) {
    for (var j = columns.length - 1; j >= 0; j--) {
      arr[i].splice(columns[j], 1);
    }
  }
}

// 示例用法
var arr = [
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9, 10, 11, 12]
];

var columnsToExtract = [1, 3];
var extractedColumns = extractColumns(arr, columnsToExtract);
console.log(extractedColumns);
// 输出: [[2, 4], [6, 8], [10, 12]]

removeColumns(arr, columnsToExtract);
console.log(arr);
// 输出: [[1, 3], [5, 7], [9, 11]]