JavaScript: setInterval()

Syntax is Below:

    setInterval(() => {
        console.log(`Hi There!`);
        }, 4000);
        // Console.logs "Hi There" every 4 seconds (4000 milliseconds)

        or 

        setInterval(function(){
        console.log(`Hi There!`);
        }, 8000);
        // Console.logs "Hi There" every 8 seconds (8000 milliseconds)

The code used for index.php is below:

<!DOCTYPE html>
<html lang="en">
<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">
    <link rel="stylesheet" href="../styles.css">
    <title>JavaScript: setInterval()</title>
</head>
<body>

<h1>JavaScript: setInterval()</h1>

<input type="number" name="number" id="number" placeholder="Enter Interval in Seconds">
<button id="submit">Submit</button>

<p>Syntax is Below:</p>
    <pre>
    setInterval(() => {
        console.log(`Hi There!`);
        }, 4000);
        // Console.logs "Hi There" every 4 seconds (4000 milliseconds)

        or 

        setInterval(function(){
        console.log(`Hi There!`);
        }, 8000);
        // Console.logs "Hi There" every 8 seconds (8000 milliseconds)

</pre>

<div id="fill-div"></div>

<script>

const submit = document.getElementById('submit');
const fillDiv = document.getElementById('fill-div');
const number = document.getElementById('number');

function Interval(seconds){

    const milliseconds = seconds * 1000;

    setInterval(() => {

        console.log("Hi There");
        console.log(milliseconds);
        fillDiv.innerHTML = fillDiv.innerHTML + `Interval Selected: ${seconds} Seconds<br>`
    }, milliseconds);
}

submit.addEventListener('click', () => {
    Interval(number.value);
});

</script>
<?php
    include('../show_code.php');
    show_code('index.php');
?>  
</body>
</html>