How to One TextBox Value Move to another TextBox unsing JavaScript

Question

I Have using This Format but i need Correct answer only This Method used not accurate answer

JS CODE:

<script>
    $(function(){
    $("#ctl00_ContentPlaceHolder1_chksa").on('ifChecked',function(event){
    $("#<%=txtSAddress1.ClientID%>").val($("#<%=txtAddress1.ClientID%>").val());
    $("#<%=txtSAddress2.ClientID%>").val($("#<%=txtAddress2.ClientID%>").val());
    $("#<%=txtSCity.ClientID%>").val($("#<%=txtCity.ClientID%>").val());
    $("#<%=txtSState.ClientID%>").val($("#<%=txtState.ClientID%>").val());
    $("#<%=txtSCountry.ClientID%>").val($("#<%=txtCountry.ClientID%>").val());
    $("#<%=txtSPincode.ClientID%>").val($("#<%=txtPincode.ClientID%>").val());
    $("#<%=txtSEmailID.ClientID%>").val($("#<%=txtEmailID.ClientID%>").val());
    $("#<%=txtSContactNo.ClientID%>").val($("#<%=txtPhoneNo.ClientID%>").val());

    }); 
 <script>

Answer 1

Assuming ctl00_ContentPlaceHolder1_chksa to be checkbox .

You can use change event and test if checkbox is checked copy the values

$(function() {
    $("#ctl00_ContentPlaceHolder1_chksa").on('change', function(event) {
        if (this.checked) {
            $("#<%=txtSAddress1.ClientID%>").val($("#<%=txtAddress1.ClientID%>").val());
            $("#<%=txtSAddress2.ClientID%>").val($("#<%=txtAddress2.ClientID%>").val());
            $("#<%=txtSCity.ClientID%>").val($("#<%=txtCity.ClientID%>").val());
            $("#<%=txtSState.ClientID%>").val($("#<%=txtState.ClientID%>").val());
            $("#<%=txtSCountry.ClientID%>").val($("#<%=txtCountry.ClientID%>").val());
            $("#<%=txtSPincode.ClientID%>").val($("#<%=txtPincode.ClientID%>").val());
            $("#<%=txtSEmailID.ClientID%>").val($("#<%=txtEmailID.ClientID%>").val());
            $("#<%=txtSContactNo.ClientID%>").val($("#<%=txtPhoneNo.ClientID%>").val());
        }
    });
});