当我在javascript中有一个对象时，如何创建二维数组？

var twoDimensionalArray = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];

var rows = 3;
var columns = 3;
var twoDimensionalArray = [];
for (var i = 0; i < rows; i++) {
  twoDimensionalArray[i] = [];
  for (var j = 0; j < columns; j++) {
    twoDimensionalArray[i][j] = i + j;
  }
}

var rows = 3;
var columns = 3;
var twoDimensionalArray = new Array(rows);
for (var i = 0; i < rows; i++) {
  twoDimensionalArray[i] = new Array(columns);
}

var element = twoDimensionalArray[0][0];