isNaN not firing until 2 characters are typed in
<p>My HTML code is:</p>

<pre><code>&lt;input onKeyPress="validateA(this.value)" type="text" id="AAA" name="AAA" size="10" placeholder="A"&gt;
&lt;span id="aspan" class="validate"&gt;  &lt;/span&gt;
</code></pre>

<p>and my Javascript is:</p>

<pre><code>function validateA(valueOfAAA) {
if (isNaN(valueOfAAA)) {
    document.getElementById('aspan').innerHTML="Please enter a numerical value.";

}
else {
    document.getElementById('aspan').innerHTML="";
}

}
</code></pre>

<p>To clarify, my question is:</p>

<p>Why is the <code>innerHTML="Please enter a numerical value."</code> not firing until two letters OR numbers are typed into my input box?</p>
