why i cannot replace value of a hidden input?

i have a hidden input like this:

<input type="hidden" id="selectedItem" value="1,1,1," name="selectedItem"/>

and i want to replace some values of it to:

value="9,9,9"

i tried to used

document.getElementById('selectedItem').value = document.getElementById('selectedItem').value.re开发者_JAVA百科place(/1/gi,'9')

or

document.getElementById('selectedItem').value = document.getElementById('selectedItem').value.replace('1','9')

but it didnot work. Please someone tells me why and give me some solutions. Thank You

Why not use jquery? Something like the following:

$('input#selectedItem').value('9,9,9');

$("#selectedItem").val("9,9,9");
//or
$("#selectedItem").val($("#selectedItem").val().replace(/1/gi,'9')); 

It works just fine for me: http://jsfiddle.net/QRHTL/

It would be a bit cleaner with jQuery though:

$('#selectedItem').val($('#selectedItem').val().replace(/1/gi,'9'));

Do you have another element on your page with id="selectedItem"? If so, document.getElementById("selectedItem") might return that instead of the hidden form input you're expecting it to.