Added a few notes regarding JavaScript

doc/tut2.txt

@@ -990,3 +990,17 @@ generated by `treeRepr <macros.html#treeRepr>`_. If at the end of the this
 example you add ``echo treeRepr(result)`` you should get the same output as
 using the ``dumpTree`` macro, but of course you can call that at any point of
 the macro where you might be having troubles.
+
+
+Compilation to JavaScript
+=========================
+
+Nim code can be compiled to JavaScript. However in order to write
+JavaScript-compatible code you should remember the following:
+- ``addr`` and ``ptr`` have slightly different semantic meaning in JavaScript.
+  It is recommended to avoid those if you're not sure how they are translated
+  to JavaScript.
+- ``cast[T](x)`` in JavaScript is translated to ``(x)``.
+- ``cstring`` in JavaScript means JavaScript string. It is a good practice to
+  use ``cstring`` only when it is semantically appropriate. E.g. don't use
+  ``cstring`` as a binary data buffer.