JavaScript isNaN function
<p>I am using isNan functionto check if entered value is a number:</p>

<pre><code>if(isNaN(num)) {
    alert('I am not a number');
}
else {
//
     }
</code></pre>

<p>However, if entered value is, for example, "5748hh" it is understandable like a number and return <code>false</code>. What is wrong?</p>
