How to make your checkbox to either choose one or two fields?

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jQuery

I am struggling to find a way to make my checkbox to either choose either one or two nor combination. What the code does currently allows one to select checkbox at a time and you can download the file format. I want to find a way that is possible if a user select neither one, two or combination of the checkbox be able to download the file format based on my given code below that have attempted to write.

What I have tried:

<div class = "custom-control custom-checkbox">
  <input type="checkbox" class ="custom-control-input" id="temperature">
    <label class = "custom-control-label" for="temperature">Temperature</label>
    </div>
    
 <div class = "custom-control custom-checkbox">
 <input type = "checkbox" class="custom-control-input" id="illuminance">
   <label class = "custom-control-label" for = "illuminance">Illuminance</label>
  </div>   
 <div class ="custom-control custom-checkbox">
 <input type ="checkbox" class="custom-control-input" id="button-state">
   <label class ="custom-control-label" for = "button-state">Button-State</label>
    
<!---Downloading File using 
Jquery with Buttons---->
  <div class="form-group"><br>
  <div class="col-md-1.9 text-center">
   <button id="download" name="download" class="btn btn-warning">Download</button><br>
    </div> 
  </div>

 $(function() {
    $("#download").click(function(e){
    e.preventDefault();
      if($('temperature').is(':checked')){}
      if($('illuminance').is(':checked')){}
      if($('button-state').is(':unchecked')){}
      window.open('https://api.thingspeak.com/channels/899906/feeds.csv?start=2019-11-19%2019:11:19&end=2019-11-20%2019:11:20');
    });
  
  });