<!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Documento sin título</title> </head> <body> <form name="form1" id="form1"> <select name="dianac" id="dianac" size="1"> <option value="1">01</option> <option value="2">02</option> <option value="3">03</option> <option value="4">04</option> <option value="5">05</option> <option value="6">06</option> <option value="7">07</option> <option value="8">08</option> <option value="9">09</option> <option value="10">10</option> <option value="11">11</option> <option value="12">12</option> <option value="13">13</option> <option value="14">14</option> <option value="15">15</option> <option value="16">16</option> <option value="17">17</option> <option value="18">18</option> <option value="19">19</option> <option value="20">20</option> <option value="21">21</option> <option value="22">22</option> <option value="23">23</option> <option value="24">24</option> <option value="25">25</option> <option value="26">26</option> <option value="27">27</option> <option value="28">28</option> <option value="29">29</option> <option value="30">30</option> <option value="31">31</option> </select> <select name="mesnac" id="mesnac" size="1"> <option value="0">Enero</option> <option value="1">Febrero</option> <option value="2">Marzo</option> <option value="3">Abril</option> <option value="4">Mayo</option> <option value="5">Junio</option> <option value="6">Julio</option> <option value="7">Agosto</option> <option value="8">Setiembre</option> <option value="9">Octubre</option> <option value="10">Novienbre</option> <option value="11">Diciembre</option> </select> <input name="anonac" id="anonac" type="text" size="5" maxlength="4" onkeyup= "if(isNaN(this.value)){this.value=this.value.substring(0,this.value.length-1)}"> <input name="edad" type="text" size="5" id="edad" onfocus="var y=anonac.value,e=0;while(new Date(++y,mesnac.value,dianac.value)<new Date()){if(e>110){alert('el año es incorrecto');return this.value='';}e++;}this.value=e"> </form> </body> </html>