HTML checkbox to Javascript form

I am (still) working on creating sidebar input for a Sheets add-on I'm developing. My current challenge is allowing a textbox and a checkbox to be passed from the form to my function.

The textbox works and successfully passes the variable. The checkbox I'm not as clear on. I need to turn the checkbox into a boolean.

The relevant html:

<p>
  <input type="text" id="datepicker">
  </p>
  <p>
  Include pledge?<br>
    <input type="checkbox" name="pledge[]" id="pledgeCheck" value="true">Yes<br>
  <input type="radio" name="pledge" id="Off">No
  </p>
          <p>
            <input type="button" name="createdate" value="Create" onClick="google.script.run.create(document.getElementById('datepicker').value,document.getElementById('pledgeCheck').value)" />
          </p>

function create(datepicker,pledge) {

  //important vars
  var responses = ss.getSheetByName("Form Responses");
  var bulletin = ss.getSheetByName(todayDate);
  var todayDate=datepicker;
  var pledgeCheck=pledge;
  Logger.log(pledgeCheck);
  

currently the pledge feeds back as undefined.