ParseFloat goes NaN
<p>Hello everyone i have this code</p>

<pre><code>function computeChange(){
var change;
var amountDue = parseFloat(document.getElementById("amountDue").value);
var amountReceive = parseFloat(document.getElementById("amountReceive").value);
change = amountReceive - amountDue;
document.getElementById('amountChange').innerHTML = change;
}



&lt;td&gt;Total Amount&lt;/td&gt;
&lt;td&gt;Php:&lt;span id="amountDue"&gt;&lt;?php echo $sum; ?&gt;&lt;/span&gt;&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;
&lt;td&gt;Amount Paid&lt;/td&gt;
&lt;td&gt;&lt;input type="number" id="amountReceive" required="required" maxlength="4" size="4" onKeyUp="computeChange()"&gt;&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;
&lt;td&gt;Change&lt;/td&gt;
&lt;td&gt;Php:&lt;span id="amountChange"&gt;&lt;/span&gt;&lt;/td&gt;
&lt;/tr&gt;
</code></pre>

<p>on the total amount is a decimal<br>
on the amount paid input type=text</p>

<p>So the problem is if i enter something in the text box the span on change goes <code>NaN</code></p>
