console
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<style>
table,tr,td{
border:1px solid blue;
}
#ok,.td,#clear,#last{
text-align:center;
}
</style>
</head>
<body>
<table>
<tr>
<td colspan="5" id="show">0</td>
</tr>
<tr>
<td class="td" id="zero">0</td>
<td class="td">.</td>
<td id="last"><</td>
<td id="clear" colspan="2">c</td>
</tr>
<tr>
<td class="td">1</td>
<td class="td">2</td>
<td class="td">3</td>
<td class="td">+</td>
<td class="td">-</td>
</tr>
<tr>
<td class="td">4</td>
<td class="td">5</td>
<td class="td">6</td>
<td class="td">*</td>
<td class="td">/</td>
</tr>
<tr>
<td class="td">7</td>
<td class="td">8</td>
<td class="td">9</td>
<td id="ok" colspan="2">=</td>
</tr>
</table>
<script>
var oTd = document.getElementsByClassName("td");
var oK = document.getElementById("ok");
var oShow = document.getElementById("show");
var oClear = document.getElementById("clear");
var run = '';
oK.onclick=function(){
if(run!==""){
oShow.innerHTML = eval(run);
}
if(oShow.innerHTML!=="0"){
run = show.innerHTML;
}
}
oClear.onclick=function(){
run = '';
show.innerHTML = '0';
}
for(var i = 0;i<=oTd.length;i++){
oTd[i].index = i;
oTd[i].onclick=function(){
run += oTd[this.index].innerHTML;
oShow.innerHTML = run;
};
}
</script>
</body>
</html>