Set CRM Date Field to Empty

I have a check box and a date field on the form. The requirement is to display the System Date in the date field when the check box is checked by the user and to clear the date field when the check box is unchecked by the user. Although the user has unchecked the check box and saved the form it displays the previously saved date by the user. I used the following code to save it.

Following code will solve the problem and will set it to Empty when it saved.

      //get the value of Reviewed by Manager checkbox
    var ReviewedManager = crmForm.all.cpms_reviewedbymanager.DataValue;

    //if Reviewed by Manager chekbox is checked
    if (ReviewedManager == true)
    {
        //set the Date Reviewed by  to system date
        crmForm.all.cpms_datereviewedbymanager.Disabled = false;
        crmForm.all.cpms_datereviewedbymanager.DataValue = new Date();
    }
    else
    {
        crmForm.all.cpms_datereviewedbymanager.DataValue = null;
        crmForm.all.cpms_datereviewedbymanager.ForceSubmit = true;
        crmForm.all.cpms_datereviewedbymanager.Disabled = true;
    }