JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" placeholder="n" id="n">
<input type="button" value="calc" id="calc">

JavaScript

var k = 100500;
    document.getElementById('calc').addEventListener('click', function(e) {
        var input = document.getElementById('n'),
        val = input.value;
        input.value = val * k
    }, false);