JSFiddle - React, Tailwind, and code Playground

HTML

<table style="border:1px solid purple">
    <tr>
    <th style="font-size:9px;">COST</th>
    <th style="font-size:9px;">QTY</th>
    <th style="font-size:9px;">TOTAL</th>
    </tr>
    
    <tr id="Tr1">
    
    <td><input class="price" type="text" name="price[]" value="100.00"></td>
    <td><input class="qty" type="text" name="qty[]" ></td>
    <td><input type="text" class="output" name="output[]"></td>
    </tr>
    <tr id="Tr2">
    <td><input class="price" type="text" name="price[]" value="100.00"></td>
    <td><input class="qty" type="text" name="qty[]" ></td>
    <td><input type="text" class="output" name="output[]"></td>
    </tr>
    <tr id="Tr3">
   <td><input class="price" type="text" name="price[]" value="100.00"></td>
    <td><input class="qty" type="text" name="qty[]" ></td>
    <td><input type="text" class="output" name="output[]"></td>
    </tr>
    <tr id="Tr4">
   <td><input class="price" type="text" name="price[]" value="100.00"></td>
    <td><input class="qty" type="text" name="qty[]" ></td>
    <td><input type="text" class="output" name="output[]"></td>
    </tr>
  
 

</table>

JavaScript

$(document).ready(function() {
    $(this).keyup(function() {
        var grandTotal = 0;
        $("input[name='price[]']").each(function (index) {
            var price = $("input[name='price[]']").eq(index).val();
            var qty = $("input[name='qty[]']").eq(index).val();
            var output = parseInt(price) * parseInt(qty);
            
            if (!isNaN(output)) {
				$("input[name='output[]']").eq(index).val(output);
            }
        });
    });
});