JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html>
<head>
<script type='text/javascript'>

function check()
{
   var value = document.getElementById("txtin").value;
   if ((value in [,1,2,3]))
     alert("Do SomeThing");
}

</script>
</head>
<body>
    <a href="#" onclick='check()'>check</a>
    <input type="text" id="txtin"/>
</body>
</html>