Hello World Javascript Component

Mission Control: "Ok you are a go"
Ship: "Yea, we see the earth now!"

Here is a quick and dirty example of how to create a Hello World javascript component.
It is using the nsISample code posted here.
This example shows how it is done on unix.
Windows and Mac will be added.

Sample Hello interface source file
Create a file called nsIHello.idl then put the code below inside.
You can use the uuid(IID) below but what you need to do for your
own interfaces is generate a unique number.
On windows you can use

On unix:
$ uuidgen
Using irc, connect to and type in
/join #mozilla
/msg mozbot uuid

#include "nsISupports.idl"

[scriptable, uuid(2484a682-3630-4bf5-95f1-4ba6353a0874)]
interface nsIHello : nsISupports
    attribute string yourName;
    void write();
    void change(in string aValue);

Sample JS implementation source file
Then create a file called nsHello.js and put this inside.


function MyComponent() {}

MyComponent.prototype = {

    get yourName()        { return this.value; },
    set yourName(aName) { return this.value = aName; },

    write: function () { dump("Hello " + this.value + "\n"); },

    change: function (aValue) { this.value = aValue; },

    QueryInterface: function (iid) {

        if (!iid.equals(Components.interfaces.nsIHello) 
				&& !iid.equals(Components.interfaces.nsISupports))
            throw Components.results.NS_ERROR_NO_INTERFACE;
        return this;

    value : "a default value"


var myModule = {

    firstTime  : true,

    registerSelf: function (compMgr, fileSpec, location, type) {

        if (this.firstTime)
            dump("*** first time registration of Hello World JS component\n");
            this.firstTime = false;
            throw Components.results.NS_ERROR_FACTORY_REGISTER_AGAIN;

        dump(" ***** Registering: HELLO WORLD JS component! ****\n");
                                          "My JS Component",
                                          this.myProgID, fileSpec,
                                          location, true, true,

    getClassObject: function (compMgr, cid, iid) {

        if (!cid.equals(this.myCID))
            throw Components.results.NS_ERROR_NO_INTERFACE;

        if (!iid.equals(Components.interfaces.nsIFactory))
            throw Components.results.NS_ERROR_NOT_IMPLEMENTED;

        return this.myFactory;

    myCID: Components.ID("{2484a682-3630-4bf5-95f1-4ba6353a0874}"),

    myProgID: "hello_world_component", // the proper format for this would be;1

    myFactory: {

        createInstance: function (outer, iid) {
            dump("CI: " + iid + "\n");
            if (outer != null)
                throw Components.results.NS_ERROR_NO_AGGREGATION;

            return (new MyComponent()).QueryInterface(iid);

    canUnload: function(compMgr) {
        dump("****** Unloading: HELLO WORLD JS component! ****** \n");
        return true;

function NSGetModule(compMgr, fileSpec) { return myModule; }


Compiling an xpidl interface

First you will need to set the path of your xpidl compiler in your environment.
Which is located in your mozilla source tree.


Here is the output of my unix session starting with these two source files from above:

$ ls
nsIHello.idl  nsHello.js

$ PATH=$PATH:/home/petejc/MOZILLA/mozilla/xpcom/typelib/xpidl

$ echo $PATH

$ xpidl --help
ERROR: must specify output mode
Usage: xpidl [-m mode] [-w] [-v] [-I path] [-o basename] filename.idl
       -a emit annotations to typelib
       -w turn on warnings (recommended)
       -v verbose mode (NYI)
       -I add entry to start of include path for ``#include "nsIThing.idl"''
       -o use basename (e.g. ``/tmp/nsIThing'') for output
       -m specify output mode:
          header        Generate C++ header            (.h)
          typelib       Generate XPConnect typelib     (.xpt)
          doc           Generate HTML documentation    (.html)
          java          Generate Java interface        (.java)

$ XPIDL_INC=/home/petejc/MOZILLA/mozilla/xpcom/base export XPIDL_INC
$ echo $XPIDL_INC

$ xpidl -m typelib -w -v -I $XPIDL_INC \
> -o nsIHello nsIHello.idl

$ ls
nsIHello.idl  nsIHello.xpt  nsHello.js

$ cp nsIHello.xpt nsHello.js \
> /home/petejc/MOZILLA/mozilla/dist/bin/components/

Testing your interface
When you run xpcshell the result should look something like this:

$ cd /home/petejc/MOZILLA/mozilla/dist/bin/
$ js
Type Manifest File: /home/petejc/MOZILLA/mozilla/dist/bin/components/xpti.dat
nsNativeComponentLoader: autoregistering begins.
nsNativeComponentLoader: autoregistering succeeded
 ***** Registering: HELLO WORLD JS component! ****
nNCL: registering deferred (0)
js> const Hello=new Components.Constructor("hello_world_component", "nsIHello");
js> var hello=new Hello();
CI: {2484a682-3630-4bf5-95f1-4ba6353a0874}
js> for(var list in hello)
js> hello.yourName;
a default value
js> hello.yourName="Pete";
js> hello.write();
Hello Pete
js> hello.change("Brian");
js> hello.write();
Hello Brian
js> hello.yourName;

CanUnload_enumerate: skipping native
From a web page you can do this: <script language="javascript">"UniversalXPConnect"); var Hello=new Components.Constructor("hello_world_component", "nsIHello"); var h=new Hello(); for(var list in h) document.write(list+"<br>\n"); </script> Enjoy!


User Notes: [?]

If you do not get a response to a question posted in this forum, please try sending a message to the project's mailing list or to the project owner directly.

[1] Submitted by: Dan Parent on Monday February 12th 2001

In order for the last javascript part to work properly Mozilla had to be restarted.

[2] Submitted by: pete collins on Monday February 12th 2001

Yes. The components are registered when mozilla launches. If there is any new files added to the components dir, they are registered and made available when started or restarted.


[3] Submitted by: Scott on Saturday March 16th 2002

why the hell did you make it so complex.

[4] Submitted by: dirk on Friday January 3rd 2003

great work! - dl /

[5] Submitted by: Diseño on Monday March 17th 2003

Hi from Spain!!

[6] Submitted by: buscadores on Friday March 21st 2003

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[7] Submitted by: jonh on Friday April 11th 2003

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[12] Submitted by: motilla on Tuesday May 13th 2003

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[13] Submitted by: adwod on Tuesday May 13th 2003


[14] Submitted by: Harald on Thursday May 15th 2003

hello world

[15] Submitted by: complejo on Friday May 16th 2003

good site

[16] Submitted by: motilla on Friday May 16th 2003

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[17] Submitted by: adwod on Friday May 16th 2003


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[21] Submitted by: Diseño web on Friday August 1st 2003

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[24] Submitted by: Alex on Sunday August 31st 2003

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/ /

/ /


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