How to change the value of check box when it is checked or unchecked

Question

Hello guys here the problem. I want to perform a different calculation based on the check box.

<div>
 COD: <input type="checkbox" id="trigger" name="question" >
</div>

Here is the javascript for calculating the price of the item the problem is that i dont know how can i do the else if method

<script>
    $("#price,#quant,#shipment").keyup(function () {
      if(+myFunction3() =="" )
      {
        $('#demo').val(0);
      }
      else if($('#trigger')=="checked") //this is the problem
      {
        $('#demo').val($('#price').val() * $('#quant').val() ;
      }
      else
      {
      $('#demo').val($('#price').val() * $('#quant').val() + +myFunction3());
     }
  });
  </script>

Advance thank you guys.

Answer 1

Using jQuery you could do:

else if($('#trigger:checked').length > 0)

or

else if($('#trigger').is(':checked'))

If you want to re-run your calculation when a user checks or un-checks the checkbox, you could run the same code you run on the keyup function on:

$('#trigger').change(function() {
  ...
})