title: difference between for..in and for loops, and counter declaration
body: <p>the difference (speed, performace, side effects, ...) between implementations of the <strong><code>for</code></strong> loop:</p>
  
  <p>between</p>
  
  <pre><code>var i;
  for(i = 0; i &lt; length; i++){ //Do something}
  // more code
  </code></pre>
  
  <p>and </p>
  
  <pre><code>for(var i = 0; i &lt; length; i++){ //Do something}
  // more code
  </code></pre>
  
  <p>and</p>
  
  <pre><code>for(i = 0; i &lt; length; i++){ //Do something}
  // more code
  </code></pre>
  
  <p>and between</p>
  
  <pre><code>var e;
  for( e in array){ //Do something}
  // more code
  </code></pre>
  
  <p>and</p>
  
  <pre><code>for(var e in array){ //Do something}
  // more code
  </code></pre>
  
  <p>and </p>
  
  <pre><code>for(e in array){ //Do something}
  // more code
  </code></pre>