Version 1?

sources/scripts/pos.js

@@ -12,4 +12,9 @@ function Pos(x,y)
   {
     return new Pos(this.x - pos2.x,this.y - pos2.y)
   }
+
+  this.is_equal = function(pos2)
+  {
+    return pos2.x == this.x && pos2.y == this.y;
+  }
 }