Unable to Retrieve Value of CheckboxList from Javascript

In my .ascx page, I am unable to retrieve the value of a CheckboxList via javascript.

The error is that the value is undefined.

Javascript:

var schedule = document.getElementById("<%=ddlExecutionSchedule.ClientID%>").value;

//Value of schedule was logged as 'undefined'
console.log("Log 1. schedule = "+schedule);

CheckboxList element:

<div class="form-group" id="executionSchedule">
    <label class="control-label col-md-2" id="lblExecutionSchedule">Execution Schedule</label>
    <div class="col-md-3">
        <div class="input-group">
            <asp:CheckboxList ID="ddlExecutionSchedule" ClientIDMode="Static" CssClass="chkLabel" runat="server" AutoPostBack="false" CellPadding="5" CellSpacing="5" RepeatDirection="Horizontal" RepeatLayout="Table" onchange="ToggleExecutionSchedule(this)" >
                <asp:ListItem Text="Daily" Value="Daily"></asp:ListItem>
                <asp:ListItem Text="Weekly" Value="Weekly"></asp:ListItem>
                <asp:ListItem Text="Monthly" Value="Monthly"></asp:ListItem>
            </asp:CheckboxList>
        </div>
    </div>
</div>

Any help would be appreciated.


EDIT:

After referencing from post How to get value of selected checkboxlist items using javascript in asp.net,

I added in getElementsByTagName after getElementById.

var scheduleSelected = schedule.getElementsByTagName('input');

But hit the following error:

Uncaught TypeError: Cannot read property 'getElementsByTagName' of undefined at SaveCheck