Why this function return Nan error?
<p>When I click "+ 1", then in the "0" appears "NaN". Why ?</p>

<p>HTML:</p>

<pre><code>&lt;table&gt;
&lt;tr&gt;&lt;td id="run"&gt;0&lt;/td&gt;&lt;/tr&gt;
&lt;/table&gt;
&lt;a href="#" onclick="plus();"&gt;+ 1 &lt;/a&gt;
</code></pre>

<p>JS:</p>

<pre><code>function plus(){
document.getElementById("run").innerHTML = ( document.getElementById("run").value + 1 );
}
</code></pre>
