JavaScript in webpage not working

I have this webpage

<input id="show" style="display: inline;" type="button" onclick="document.getElementById('hash').value = hex_sooml('M77LNALA');" value="Show Password">

<input style="display: inline;" id="hash" size="50" type="text">

<script type="text/javascript">
function hex_soom1(pass)
{
return pass;
}
</script>

When I click the button nothing happens. Why?