title: Check if string zero, zero, empty string, null
body: <p>in PHP:</p>
  
  <pre><code>$var=0;
  $var="";
  $var="0";
  $var=NULL;
  </code></pre>
  
  <p>to verify if $var is 0 or "0" or "" or NULL</p>
  
  <pre><code>if (!$var) {...}
  </code></pre>
  
  <p>in jQuery/JavaScript:</p>
  
  <pre><code>$var=0;
  $var="";
  $var="0";
  $var=NULL;
  </code></pre>
  
  <p><code>if (!$var)</code> works for every value except for "0"</p>
  
  <p>Is there a general way in JavaScript/jQuery to check all kinds of those empty/null/zero values, exactly like php does?</p>