JSFiddle - React, Tailwind, and code Playground

HTML

<input class="text big" name="amount" type="text" min="1" max="300000" id="input1" onkeyup="calc()" required />
				<br />
				<br />
				<input class="text big" type="text" name="output" id="output" value="">

JavaScript

function calc() {
    $cp1 = 4;
    var textValue1 = document.getElementById('input1').value;
    var textValue2 = $cp1;

    document.getElementById('output').value = textValue1 * textValue2;
};