JSFiddle - React, Tailwind, and code Playground

HTML

<table>
     <tbody>        
     <tr id="person_bmi">
        <td>Jack</td>
        <td><input name="weight" type="text" class="span1 weight" maxlength="5"></td>
        <td><input name="height" type="text" class="span1 height" maxlength="5"></td>
        <td><input name="bmi" type="text" class="span1 bmi" readonly></td>       
      </tr>

    <tr id="person_bmi">
        <td>Michael</td>
        <td><input name="weight" type="text" class="span1 weight" maxlength="5"></td>
        <td><input name="height" type="text" class="span1 height" maxlength="5"></td>
        <td><input name="bmi" type="text" class="span1 bmi" readonly></td>       
      </tr>
</tbody>
</table>

JavaScript

$(".weight, .height").keyup(function() {
    var row = $(this).parent().parent(),
        weight = $('input[name=weight]', row).val(),
        height = $('input[name=height]', row).val();
         var bmi = weight *703 / height * height;
    $('.bmi', row).val(isNaN(bmi) ? '' : bmi);
});