How can I validation single dropdown inside grid view using JavaScript?

function Validate() {

var flag = true;
var dropdowns = new Array(); //Create array to hold all the dropdown lists.
var gridview = document.getElementById('<%=gv_accounting.ClientID%>'); //GridView1 is the id of ur gridview.
dropdowns = gridview.getElementsByTagName('select'); //Get all dropdown lists contained in GridView1.
for (var i = 0; i < dropdowns.length; i++) {
if (dropdowns.item(i).value == '0') //If dropdown has no selected value
{
flag = false;
break; //break the loop as there is no need to check further.
}
}
if (!flag) {
alert('Please select value in each dropdown');
}
return flag;

}