JSFiddle - React, Tailwind, and code Playground

HTML

<label>Value 1</label>
    <input type="number" id="value1"></input>
    
    <label>Value 2</label>
    <input type="number" id="value2"></input> <br>  
    
    <button type="button" onclick="doMaths();">Calculate</button><br>
    
    <label>Result</label>
    <input type="number" id="result"></input>

JavaScript

function doMaths() {
    var val1 = document.getElementById("value1");
    var val2 = document.getElementById("value2");
    var result = document.getElementById("result");
    
    result.value = parseInt(val1.value) + parseInt(val2.value);
}