var headertext = []; var headers = document.querySelectorAll("thead"); var tablebody = document.querySelectorAll("tbody"); for (var i = 0; i < headers.length; i++) { headertext[i]=[]; for (var j = 0, headrow; headrow = headers[i].rows[0].cells[j]; j++) { var current = headrow; headertext[i].push(current.textContent); } } for (var h = 0, tbody; tbody = tablebody[h]; h++) { for (var i = 0, row; row = tbody.rows[i]; i++) { for (var j = 0, col; col = row.cells[j]; j++) { col.setAttribute("data-th", headertext[h][j]); } } }