HTML code:

    <input type="text" id="iop">
    <button onclick=suh()>Calculate</button>
    <p id="final"></p>

Javascript code:

let iop=document.getElementById('iop').value;
let num=parseFloat(iop);
function suh(){
    document.getElementById('final').innerHTML=`The square of the number entered is ${num}`;
}

The output is: The square of the number entered is NaN