radio.html

<!DOCTYPE html>
<input lang="en">
<html>
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Radio</title>
  </head>
  <body>
    
    <h2>Mainpualte radio buttons using DOM</h2>
    
    <input id="rd1" name="grp1" type="radio" value="Blockchain">Blockchain</input>
    <input id="rd2" name="grp1" type="radio" value="Solidity">Solidity</input> 
    
    <button onclick="fn1()" id="btn1">Click Here</button>
    <script>
      function fn1(){
        let rd1= document.getElementById("rd1");
        let rd2=document.getElementById("rd2");
        if(rd1.checked== true){
            alert("the topic for today's class is "+ rd1.value);
        }else{
            alert("the topic for today's class is "+ rd2.value)
        }

      }
    </script>
  </body>
</html>