In the row index (iRow), you can use the rowIndex property of the DOM object that represents the row row <tr>. So you just need to get the DOM of the string. If it rowIddoes not contain metacharacters , you can only do the following
var iRow = $('#' + rowId)[0].rowIndex;
jqID, :
var iRow = $('#' + $.jgrid.jqID(rowId))[0].rowIndex;