JSFiddle - React, Tailwind, and code Playground

HTML

Enter First Number :
<br>
<input type="text" id="Text1" name="TextBox1">
<br>Enter Second Number :
<br>
<input type="text" id="Text2" name="TextBox2">
<br>Result :
<br>
<input type="text" id="txtresult" name="TextBox3">
<br>
<input type="button" name="clickbtn" value="Display Result" onclick="add_number()">

JavaScript

function add_number() {
               
                var first_number = parseInt(document.getElementById("Text1").value);
                var second_number = parseInt(document.getElementById("Text2").value);
                var result = first_number + second_number;
     
                document.getElementById("txtresult").value = result;
            }