title: trigger an event when an element reaches a position on the screen
body: <p>I would like to trigger some functions according to a position of an element. This element's position changes every tenth second.  There is two dozens functions to trigger.</p>
  
  <p>I thought about this pseudo-code :</p>
  
  <pre><code>When element position changes{
    Loop through all the coordinates to see if a function can be triggered{
       if the current element position matches the function's triggering position 
           execute the function
       }
  }
  </code></pre>
  
  <p>But looping through all possible position each split seconds burdens the browser. So if there is a way to have events to do that.</p>
  
  <p>Is it possible ?</p>
  
  <p>Edit:
  After Beetroot-Beetroot comment, I must say that the element that moves only moves on an X abscissa : so just one dimension.</p>
  
  <p>It's much like a horizontal timeline moving from left to right, where some animation happen when a certain year is reached.
  However the moving speed can be increased by the user, so fixed time to trigger animation is not an option.</p>