How we can select all list box and Deselect All list box using javascript

 

And when user click Deselect All button then all item of list box deselected like

 

 

For these add listbox inside body tag and add two button Select All and Deselect All

asp:ListBox ID="lstbox" runat="server" SelectionMode="Multiple" Height="150px" Width="100px" >
            <asp:ListItem Value="1" Text ="Class 1"></asp:ListItem>
            <asp:ListItem Value="2" Text ="Class 2"></asp:ListItem>
            <asp:ListItem Value="3" Text ="Class 3"></asp:ListItem>
            <asp:ListItem Value="4" Text ="Class 4"></asp:ListItem>
            <asp:ListItem Value="5" Text ="Class 5"></asp:ListItem>
            <asp:ListItem Value="6" Text ="Class 6"></asp:ListItem>
            <asp:ListItem Value="7" Text ="Class 7"></asp:ListItem>
        </asp:ListBox>
         <button onclick="selectDeselect('lstbox', true);return false;">Select All</button>
        <button onclick="selectDeselect('lstbox', false);return false;">Deselect All</button>

And javaScript in head Tag

script>
        function selectDeselect(listid, status) {
            var listb = document.getElementById(listid);
            var len = listb.options.length;
            for (var i = 0; i < len; i++) {
                listb.options[i].selected = status;
            }
        }

      </script>

And now run the code

 

It May help Anyone!!