js实现div的切换特效上一个下一个

//下一个div
function next() {
var arr = document.getElementById('tdBjzbsx').getElementsByTagName('div');
for (i = 0; i < arr.length-1; i++) {
if ((arr[i].style.display == "block"||arr[i].style.display == "") && i <= 2) {
arr[i + 1].style.display = "block";
arr[i].style.display = "none";
}
}
}
//上一个div
function top() {
var arr = document.getElementById('tdBjzbsx').getElementsByTagName('div');
for (i = 0; i < arr.length; i++) {
if ((arr[i].style.display == "block"||arr[i].style.display == "") && i <= 3) {
arr[i - 1].style.display = "block";
arr[i].style.display = "none";
break;
}
}
}

<table>
<tr>
<td id="tdBjzbsx">
<div id="div1">
1
</div>
<div id="div2" style="display: none">
2
</div>
<div id="div3" style="display: none">
3
</div>
</td>
<td>
<input type="button" value="上一步" id="syb" name="cz2" onclick="javascript:top()" disabled="true"/></br></br>
<input type="button" value="下一步" id="xyb" name="cz3" onclick="javascript:next()"/></br></br>
</td>
</tr>
</table>