MediaWiki:Common.js

/* Any JavaScript here will be loaded for all users on every page load. */

var customizeToolbar = function() {
        /* Your code goes here */
};
 
/* Check if view is in edit mode and that the required modules are available. Then, customize the toolbar . . . */
if ( $.inArray( mw.config.get( 'wgAction' ), ['edit', 'submit'] ) !== -1 ) {
        mw.loader.using( 'user.options', function () {
                if ( mw.user.options.get('usebetatoolbar') ) {
                        mw.loader.using( 'ext.wikiEditor.toolbar', function () {
                                $(document).ready( customizeToolbar );
                        } );
                }
        } );
}

// OLD WAY - "classic toolbar"
mw.toolbar.addButton({
        imageId: 'mw-customeditbutton-myspecialbutton',
        imageFile: '//upload.wikimedia.org/wikipedia/en/3/34/Button_hide_comment.png',
        speedTip: "Title label",
        tagOpen: "<!-- ",
        tagClose: " -->",
        sampleText: "Insert comment here"
});