<input type="text" name="T1" size="20">
<input type="button" name="btn" value="if (sdiv.style.display=='none') sdiv.style.display='block';">
<div id=sdiv style="display:none"><input type="text" name="T1" size="20"></div>
<input type="button" name="btn" value="if (sdiv.style.display=='none') sdiv.style.display='block';">
<div id=sdiv style="display:none"><input type="text" name="T1" size="20"></div>
<input type="text" name="T1" size="20">
<input type="button" name="btn" value="showT1" onclick="if (sdiv.style.display=='none') sdiv.style.display='block';">
<div id=sdiv style="display:none"><input type="text" name="T1" size="20"></div>
<input type="text" name="T1" size="20">
<input type="button" name="btn" value="toggle" onclick="toggle()">
<div id=sdiv style="display:none">
</div>
<script>
var t=0;arr=['<input type="text" name="T1" size="20">','<input type="password" name="T1" size="20">']
function toggle(){
T1.outerHTML=arr[++t%arr.length]
}
</script>
<input type="text" name="T1" size="20">
<input type="password" name="T1" size="20" style='display:none'>
<input type="button" name="btn" value="toggle" onclick="toggle()">
<div id=sdiv style="display:none">
</div>
<script>
function toggle(){
var o=document.getElementsByName("T1")
for(var i=0;i<o.length;i++)
with(o[i].style)display=(display=="none"?"":"none")
}
</script>