js实现二维数组转置

var arr1 = [[30,-1,90],[70,100,-40],[39,29,6],[39,92,9]];
var arr2 = [];

var2 = [
   [30,70,39,39],
   [-1,100,29,92],
   [90,-40,6,9]
]

// 确定新bai数组du有多少zhi行
for(var i=0;i<arr1[0].length;i++){
arr2[i] = [];
}
//遍历原数组
for(var i=0;i<arr1.length;i++){
for(var j=0;j<arr1[i].length;j++){
arr2[j][i] = arr1[i][j];
  }
}

console.log(arr2);

var newArray = arr[0].map(function(col, i) {
    return arr.map(function(row) {
      return row[i];
    })
 });