How do I clear the value of hidden filed

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ASP.NET

Hello,

I've a hidden field and a textbox control. I'm setting the value of hidden field from textbox and I;ve a pipe for hidden value which is the value of textbox and another value from jquery function. whenever i click the ok button on alert box and enter a new value in textbox it is attached to old value with extra pipe. My question is how to clear the value of hidden field whenever I enter new text in textbox.

function transferValue() {

            var inputVal = document.getElementById('<%=txtHoursorAmount.ClientID %>').value;
            document.getElementById('<%=hdnAmountorHours.ClientID %>').value = document.getElementById('<%=hdnAmountorHours.ClientID %>').value + "|" + inputVal;
            alert(document.getElementById('<%=hdnAmountorHours.ClientID %>').value);
        }