title: what does `!function()` mean?
body: <p>I'm using a nice <a href="https://github.com/braincrafted/bootstrap-bundle" rel="nofollow noreferrer">bundle</a> that integrates Bootstrap with Symfony. It contains some javascript for dealing with form field collections. When I was looking at the <a href="https://github.com/braincrafted/bootstrap-bundle/blob/develop/Resources/js/bc-bootstrap-collection.js" rel="nofollow noreferrer">code</a> to see how they did it I ran across this:</p>
  <pre><code>!function($){
  
    //function body
  
  }(window.jQuery);
  </code></pre>
  <p>I'm familiar enough with javascript to recognize <code>(function(arg){})(anArg);</code> as a self-executing function, but since this lacks the enclosing parentheses I'm at a loss as to what <code>!</code> is negating.</p>
  <p>What is happening here?</p>