Código HTML:
<html> <head> <script type="text/javascript"> <!-- function crearFila() { var tabla = document.getElementById("tabla"); var fila = tabla.insertRow(1); var celda1 = fila.insertCell(0); var element1 = document.createElement("input"); element1.type = "text"; celda1.appendChild(element1); } //--> </script> </head> <body> <table id="tabla" border="1"> <tr> <td>Primera celda</td> </tr> </table> <br> <input type="button" onclick="fila()" value="Crear fila"> </body> </html>