title: Checkbox is always returning false even when checked
body: <p>ASP.NET 4.51 WebForms, jQuery 2.0.3</p>
  
  <pre><code>&lt;div class="row"&gt;
    &lt;div class="col-xs-3 col-sm-3 col-md-3"&gt;
      &lt;div class="checkbox"&gt;
        &lt;label&gt;
          &lt;asp:CheckBox ClientIDMode="Static" ID="chkAgree" runat="server" /&gt;I Agree
        &lt;/label&gt;
      &lt;/div&gt;      
      &lt;br/&gt;
      &lt;asp:CustomValidator ID="cfvAgree" runat="server" ValidationGroup="Default" ErrorMessage="Agree to terms and conditions." ClientValidationFunction="CheckTermsAndConditions" CssClass="label label-danger"&gt;&lt;/asp:CustomValidator&gt;
    &lt;/div&gt;
  </code></pre>
  
  <p>and the java script:</p>
  
  <pre><code>&lt;script type="text/javascript"&gt;
      function CheckTermsAndConditions(aSource, aArgs) {
  
          if ($('#checkbox').prop('checked')) {
              console.log("true");
              aArgs.IsValid = true;
          } else {
              console.log("false");
              aArgs.IsValid = false;
          }
  
      }
  
  &lt;/script&gt;
  </code></pre>
  
  <p>The issue is that even if the checkbox is checked it always returns false. I am sure I am missing something obvious here, but what is it?</p>