title: howto write a good Immediate execution function?
body: <p>1.often in my code</p>
  
  <pre><code>(function(){})();
  </code></pre>
  
  <p>2.often read</p>
  
  <pre><code>(function(){}.call(this));
  </code></pre>
  
  <p>there are works well. which one is better? why?</p>