Apps Script数组未按预期工作：子数组引用导致结果异常

问题现象 #

调试时发现，父数组thisArray没有执行直接赋值操作，所有元素却都变成了最后一次循环的结果：

• 预期输出：

["Pass # 1","this is some data"]
["Pass # 2","this is some data"]
["Pass # 3","this is some data"]

• 实际输出：

["Pass # 3","this is some data"]
["Pass # 3","this is some data"]
["Pass # 3","this is some data"]

复现代码 #

function debugThis(){
  var thisArray = [];
  var thisRow = [];
  var pass = 0;

  for (var i = 0; i < 3; i++) {
    pass++;
    thisRow[0] = 'Pass # ' + pass;
    thisRow[1] = 'This is some data';
    thisArray[i] = thisRow;
  }
}

问题根源 #

JavaScript中数组属于引用类型，你只创建了一个thisRow数组实例。每次循环只是修改这个实例里的元素值，然后把它的引用存入thisArray。这就导致thisArray的三个元素其实指向同一个数组对象，最后一次循环修改了这个对象的内容，所有引用它的位置自然都会显示最新值。

修复方法 #

每次循环时新建一个thisRow数组，不要复用同一个实例：

function debugThis(){
  var thisArray = [];
  var pass = 0;

  for (var i = 0; i < 3; i++) {
    pass++;
    // 每次循环创建新数组
    var thisRow = [];
    thisRow[0] = 'Pass # ' + pass;
    thisRow[1] = 'This is some data';
    thisArray[i] = thisRow;
  }
}

也可以用数组字面量简化写法，更直观：

function debugThis(){
  var thisArray = [];
  var pass = 0;

  for (var i = 0; i < 3; i++) {
    pass++;
    thisArray[i] = ['Pass # ' + pass, 'This is some data'];
  }
}

内容的提问来源于stack exchange，提问作者glenn