How to invoke a plug-in menu item via Javascript?

Question

Hi, I installed a plug-in on my Acrobat Pro v11, it shows a plug-in menu, and there's one menu item in this plug-in menu dropdown. I can manually select that menu item and it does what it's designed to do.
My question is, how do I use javascript to invoke it, to achieve the same result as when I manually select that menu item?
I tried using this "app.execMenuItem("name-of-menu-item");" under my click event of a button on the PDF form, but it didn't work.
What have I done wrong? How to make it work?
TIA

Answer 1

Thanks to all those who responded.
Actually I got it working soon after I posted the question.
However, I don't know, my trial&error way seems to be a little different from all those documents I read. 
So, I am not exactly sure if it's the correct way to do this sort of thing or not.
It certainly is not very end-user friendly IMHO.  
I will describe what I did below, if you know of a better way, please let me know, thank you.
First, I put a folder-level script in the Acrobat install folder, the so-called "app" level;
because when I used the getPath("user", "javascript") call, it returned an error without giving me the user-level path. 
Anyway, my script (the .js file) looks like this:
xyz = app.trustedFunction(
             function() {
              app.beginPriv();
              app.execMenuItem("ADBE:myxyz");
              app.endPriv();
              return;
Then, on my form's button-click event, I make a call
  xyz();
and that got it to invoke the menu item "myxyz" successfully.
But... I can't say I like my solution:
1) I don't like the .js file, because I'll have to put it in all my users' Acrobat install folders.
     Extremely inconvenient.
     Is there a way to make it work without using the folder level script???
2) The script itself, I am not sure if it makes sense or not.
     I can't say I understand all these trustFunction and Security stuff;
      it just so happened that it worked for me, but I don't know why.
      so, maybe there could be a simpler script that can also work?
3) If I put the "beginPriv()" , "execMenuItem()" and "endPriv()" lines directly in the Button-click event,
      I got an error message in the Acrobat console, something like:  "your security settings does not allow....";
      in fact, I tried many many different ways to write this Button-click script, none of them worked without the folder-level .js file.
      But I hope somebody could come up with a way to make it work without the folder-level script file....
      Is there a way to change the "security settings" without using the .js file?
4) The execMenuItem is also a headache, sorry about complaining... but... sometimes it just silently exited without doing anything,
      and without returning any error messages... how am I supposed to know what went wrong when it's so quiet?!
       Furthermore, why does it insist on taking the full name of the menu item?  I mean, why do I must put the "ADBE:" part in there?
      there's no other menu item named "myxyz", right?
      I remember Adobe's founders once said that "making our customers' lives easier" was what drove them to work everyday.
      execMenuItem() certainly didn't listen to what they said.