Uncaught TypeError: Cannot read property ‘style’ of null – JS error

I’m getting a javascript error from my console that reads:

Uncaught TypeError: Cannot read property ‘style’ of null

Does anyone know whats wrong?

Code (JS):

<script>
    function select()
    {
        document.getElementById('#iframetest').style.display='block';
    }

</script>

Code (HTML):

<iframe src="localhost/createaclass" id="iframetest"></iframe>

<div class="b" onclick="select()">