Window prompot(method) for use input text [duplicate]

please help

    <button onclick="myFunction()">Try it</button>

<p id="demo"></p>

<script>
function myFunction() {
  let person = prompt("Please enter your name", "Harry Potter");
  if (person != null) {
    document.getElementById("demo").innerHTML =
    "" + person + ""
  }
}
</script>

<input type=”text” name=”T1″ value=”javascript”

How can I add the field here?
“” + person + “”

input text value.