How to display the exponential notation of aa specified number in javascript?

Html page:

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

<p id="P9"></p>

Javascript page:

<script>

    function myFunction() {

        var num = 5.56789;

        var n = num.toExponential();

        document.getElementById("demo").innerHTML = n;

    }

</script>

Output:

5.56789e+0