Detect String which contain only spaces
<p>A  string length wich contain one space is always equal to 1:</p>

<pre><code>alert('My str length:'+ str.length);
</code></pre>

<p>The space is a caracter, ok, so:</p>

<pre><code>str="   ";
alert('My str length:'+ str.length);// My str length: 3
</code></pre>

<p>How can i make distingtion between empty string and a string which contains only spaces.
How can i detect a String which contain only spaces.</p>
