JSFiddle - React, Tailwind, and code Playground
HTML
<input type="text" name="input1" id="input1" value="5">
<input type="text" name="input2" id="input2" value=""> <a href="javascript: void(0)" onClick="calc()">Calculate</a>
<input type="text" name="output" id="output" value="">
JavaScript
$("#input2,#input1").keyup(function () {
$('#output').val($('#input1').val() * $('#input2').val());
});