title: How to detect if one element touched another
body: <p>I want to create an online webapp game like Mario. </p>
  
  <p>I have an image of a portal, and a picture of Mario. 
  I know how to move the position of the image of mario with the arrow keys. 
  What I don't know is how to respond to the event when the picture of Mario touches the portal? The images have ids of "mario" and "portal". 
  Should I use jQuery to solve this question. 
  Thanks in advance!-</p>