Problem displaying the result with my code in blogger

Yo Galera, beauty! I have a little problem. I made a code to be displayed on the page of my blog a generator of Link Me. In which the person fills out the form and at the end is generated the code for the person to copy and paste on her blog. But at the time of clicking the button and generating the code, nothing appears in the box where it should. Is it an error in my code? (He's down below.) Thanks for the help!

<h2 style="text-align: center;">
<span style="color: #3d85c6;">
Formulário</span></h2>
<br />
<table border="0" cellpadding="2" cellspacing="0" style="text-align: left; width: 580px;"><tbody>
<tr>
      <td width="225">Endereço do Blog<span style="color: red;">*</span></td>
      <td width="355"><input id="urlblog" size="60" type="text" value="http://amefuriblog.blogspot.com" /></td>
    </tr>
<tr>
      <td width="225">Link da Imagem<span style="color: red;">*</span></td>
      <td width="355"><input id="urlimg" size="60" type="text" value="http://i58.tinypic.com/amefuriblog.png" /></td>
    </tr>
<tr>
      <td width="225">Título do Blog</td>
      <td width="355"><input id="titulo" size="60" type="text" value="Amefuri Blog" /></td>
    </tr>
<tr>
      <td width="225">Descrição do Blog</td>
      <td width="355"><input id="descricao" size="60" type="text" value="Seu blog favorito de Cultura Japonesa!" /></td>
    </tr>
<tr>
      <td width="225">Largura Imagem</td>
      <td width="355"><input id="larguraimg" size="3" type="text" value="120" /> pixels</td>
    </tr>
<tr>
      <td width="225">Altura Imagem</td>
      <td width="355"><input id="alturaimg" size="3" type="text" value="60" /> pixels</td>
    </tr>
<tr>
      <td width="225">Largura Caixa de Código</td>
      <td width="355"><input id="larguracaixa" size="3" type="text" value="200" /> pixels</td>
    </tr>
<tr>
      <td width="225">Altura Caixa de Código</td>
      <td width="355"><input id="alturacaixa" size="3" type="text" value="60" /> pixels</td>
    </tr>
</tbody></table>
<div style="text-align: left;">
<br /></div>
<div style="text-align: left;">
<input class="gerarcodigo" type="button" value="Gerar Código" />
</div>
<div style="text-align: left;">
<span style="color: red;"><span style="font-weight: normal;"><br /></span></span></div>
<div style="text-align: left;">
<span style="color: red; font-size: x-small;"><span style="font-weight: normal;">*Campos Obrigatórios</span></span></div>
<h3 style="text-align: center;">
<span style="color: #3d85c6;">
Código do seu Gadget está abaixo!</span></h3>
<div style="text-align: center;">
<textarea name="resultado" onfocus="this.select()" onmouseover="this.focus()" style="height: 200px; margin: 2px; width: 580px;"></textarea>
<script type="text/javascript">
var titulo       = document.getElementById("titulo");
var descricao    = document.getElementById("descricao");
var urlblog      = document.getElementById("urlblog");
var urlimg       = document.getElementById("urlimg");
var larguraimg   = document.getElementById("larguraimg");
var alturaimg    = document.getElementById("alturaimg");
var larguracaixa = document.getElementById("larguracaixa");
var alturacaixa  = document.getElementById("alturacaixa");
var botao        = document.getElementsByClassName("gerarcodigo")[0];
var caixa        = document.getElementsByName("resultado")[0];
var inicio       = "<div align=&quot;center&quot;>
"
var fim          = "&amp;lt;/a&amp;gt;</textarea></div>
"

botao.onclick = function() {
  if (larguracaixa == "")
    {larguracaixa = 200}
  if (alturacaixa == "")
    {alturacaixa = 60}
  if (larguraimg == "")
    {codlagura = "";
     codlaguraparse = ""}
  else
    {codlargura = "width=&quot;" + larguraimg.value + "&quot;";
     codlarguraparse = "width=&amp;quot;" + larguraimg.value + "&amp;quot;"}
  if (alturaimg == "")
    {codaltura = "";
     codalturaparse = ""}
  else
    {codaltura = "height=&quot;" + alturaimg.value + "&quot;";
     codalturaparse = "height=&amp;quot;" + alturaimg.value + "&amp;quot;"}
  imagem       = "<img alt=&quot;" + titulo.value + " - " + descricao.value + "&quot; title=&quot;" + titulo.value + " - " + descricao.value + "&quot; src=&quot;" + urlimg.value + "&quot; border=&quot;0&quot; " + codlargura + " " + codaltura + "/>"
  caixacod     = "<br/><textarea onfocus=&quot;this.select()&quot; style=&quot;margin: 2px; width: " + larguracaixa.value + "px; height: " + alturacaixa.value + "px&quot; onmouseover=&quot;this.focus()&quot; name=&quot;textarea&quot;>"
  linkparse    = "&amp;lt;a href=&amp;quot;" + urlblog.value + "&amp;quot; target=&amp;quot;_blank&amp;quot;&amp;gt;"
  imagemparse  = "&amp;lt;img alt=&amp;quot;" + titulo.value + " - " + descricao.value + "&amp;quot; title=&amp;quot;" + titulo.value + " - " + descricao.value + "&amp;quot; src=&amp;quot;" + urlimg.value + "&amp;quot; border=&amp;quot;0&amp;quot; " + codlarguraparse + " " + codalturaparse + "/&amp;gt;"
  caixa.innerHTML = inicio + imagem + caixacod + linkparse + imagemparse + fim;
}
</script>
<br />
<div style="clear: both;">
</div>