使用javascript后，文本框值是否从页面以及打印窗口中消失了？

i have code that printing the selected div area after click on button print window open but problem is that when i type something into the textbox and then click on button then textbox values disppear from the page and also textbox value didn't appear in the print window?

<script>
function printDiv(divName) {
var printContents = document.getElementById(divName).innerHTML;
var originalContents = document.body.innerHTML;
document.body.innerHTML = printContents;
window.print();
document.body.innerHTML = originalContents;
}
</script>

<div id="printableArea">
<input type="text" >
</div>
<input type="button" onclick="printDiv('printableArea')" value="print a div!" />

I have altered your code to retain the textbox value:

<html>
<head>
<script>
function printDiv(divName) {
var printContents = document.getElementById(divName).innerHTML;
var originalContents = document.body.innerHTML;
var text=document.getElementById("t1").value;
document.body.innerHTML = printContents;
window.print();
document.body.innerHTML = originalContents;
document.getElementById("t1").value=text;
}
</script>
</head>
<body>
<div id="printableArea">
<input type="text" id="t1">
</div>
<input type="button" onclick="printDiv('printableArea')" value="print a div!" /> 
</body>
</html>

function printDiv(divName) {
    var inpText = document.getElementsByTagName("input")[0].value;
    var printContents = document.getElementById(divName).innerHTML;
    var originalContents = document.body.innerHTML;
    document.body.innerHTML = printContents;
    document.getElementsByTagName("input")[0].value = inpText;
    window.print();
    document.body.innerHTML = originalContents;
    document.getElementsByTagName("input")[0].value = inpText;
}