Javascript updating field

I am facing an issue where I need a value to be updated as I enter values into input fields. There is also a variable pulled from a DB in laravel framework.

I have a field which takes the total amount due and applies the eftpos surcharge to the amount as a reference for how much is required to be paid via eftpos.

I would like to update this field based on the new balance is Cash/Cheque or Scholarship amounts are added (as this are not subject to the eftpos surcharge). The idea is to ensure we are correctly applying the EFTPOS Surcharge to the eftpos amount.

HTML Code

 <table class="table">
     <thead class="text-primary">
         <th class="text-center">Method</th>
         <th class="text-center">Amount</th>
         <th></th>
     </thead>
     <tbody>
         <tr>
             <td class="text-center">EFTPOS</td>
             <td class="text-center">$ <input type="number" step="0.01" name="eftpos"></td>
             <td class="text-center"><a id="eftpos"> ${{ number_format(($income + $student->AdditionalItems->where('paid', 0)->sum('amount'))*(1+$eftpos), 2)}}</a> - Including Surcharge</td>
         </tr>
         <tr>
             <td class="text-center">Cash</td>
             <td class="text-center" id="cash">$ <input type="number" step="0.01" name="cash"></td>
             <td></td>
           </tr>
           <tr>
              <td class="text-center">Cheque</td>
              <td class="text-center" id="cheque">$ <input type="number" step="0.01" name="cheque"></td>
              <td></td>
          </tr>
          <tr>
              <td class="text-center">Scholarship</td>
              <td class="text-center" id="scholarship">$ <input type="number" step="0.01" name="scholarship"></td>
              <td></td>
          </tr>
      </tbody>
  </table>

Javascript Code

<script type="text/javascript">

window.onload = function () {
    var cash = document.getElementById('cash');
        cheque = document.getElementById('cheque');
        scholarship = document.getElementById('scholarship');
        total = document.getElementById('total');
        eftpos = 1 + {!! json_encode($eftpos, JSON_HEX_TAG) !!};

        trigFunc = function(){
            eftpos.value = (total.value - (cash.value + cheque.value + scholarship.value))*eftpos.value;
            document.getElementById('eftpos').innerHTML = eftpos.value;
            console.log(eftpos.value);
        }

    cash.onchange = trigFunc;
    cheque.onchage = trigFunc;
    scholarship.onchange = trigFunc;
}

The $eftpos is the passed by the laravel controller

Thanks in advance for your help