<form name="symbols" onsubmit="return false;">

Char:<input type="Text" size="5" maxlength="1" name="chr"><br>
Value:<input type="Text" size="5" name="val" disabled>
<input type="Submit" onclick="translate(document.symbols.chr.value);return false;">

</form>

<script language="JavaScript">
<!--
for(i=1;i<=400;i++){
	document.write(i+": &#"+i+";<br>");
}

function translate(text) {
    document.symbols.val.value = text.charCodeAt(0);
}
// -->
</script>