如果您想遍历每一行（<tr>），知道/识别该行（<tr>），并遍历每一行（<td>）的每一列（<tr>），那么这就是要走的路。

var table = document.getElementById("mytab1");
for (var i = 0, row; row = table.rows[i]; i++) {
   //iterate through rows
   //rows would be accessed using the "row" variable assigned in the for loop
   for (var j = 0, col; col = row.cells[j]; j++) {
     //iterate through columns
     //columns would be accessed using the "col" variable assigned in the for loop
   }  
}

如果您只是想遍历cell（<td>），而忽略了您所在的行，那么这就是要走的路。

var table = document.getElementById("mytab1");
for (var i = 0, cell; cell = table.cells[i]; i++) {
     //iterate through cells
     //cells would be accessed using the "cell" variable assigned in the for loop
}