Could not check the state of checkbox present in grid view

var gridData = document.getElementById("MainContent_gridRequests");

 if (gridData.rows[row].cells[7].firstChild.checked == true)

The above code is a part of my javascript code, where i try to read the state of checkbox whether it is checked or not. it throws the error undefined. this checkbox is a template field in my grid view. please let me know a solution.

Thank you!