<script type="text/javascript">

tab=[];
i=1;

while( tab.length<40 )
{
  tab.push(i);
  tab.push(i++);
}

for( i=0; i<40; i++ )
{
  document.write("<div id="+tab[i]+" style='float:left;background-color:red;width:30px;border:solid 1px black;' >"+tab[i]+"</div>");
  document.write("&nbsp;&nbsp;");
  if( i == 9 || i == 19 || i == 29 || i == 39 )
  {
    document.write("<br>");
  }
}

</script>

<style type="text/css">
div.box {
    float:left;
    margin: 1px;
    width: 30px;
    height: 20px;
    border: #000 solid 1px;
    background: #efefef;
    text-align: center;
}

div.box:hover {
    border: #000080 solid 1px;
    background: #cdcdcd;
}

div#container {
    width: 340px;
    border: 0;
    background: #fff;
}
</style>

<div id="container">

<script type="text/javascript">

var k = 0;
for( var i=0; i < 40; i++ )
{
    k = k + 0.5;
    document.write( "<div id=\"box" + i + "\" class=\"box\">" + Math.ceil(k) + "</div>" );
}

</script>

</div>

onclick=klik(this.id)

function klik(id)
{
  document.write(id);

  if( !a && !b )
  {
    a = id;
  }
  else( a && !b )
  {
    b = id;

    if( a == b )
    {
      z=u;
    }
  }

    document.write(""+a+"||");
      document.write(b);
  //writy um. testowo

}

document.getElementById("spanid").innerHTML+=id;

[HTML] pobierz, plaintext 
<span id="spanid"></span>
[HTML] pobierz, plaintext