MediaWiki:PoemButtons.js

var poemBtn = function () {
	$( '#wpTextbox1' ).wikiEditor( 'addToToolbar', {
        'section': 'main',
        'group': 'insert',
        'tools': {
            'Poem1': {
                label: 'Poem',
                type: 'button',
                icon: '//upload.wikimedia.org/wikipedia/commons/thumb/e/e1/SVG-edit_logo.svg/22px-SVG-edit_logo.svg.png',
                action: {
                    type: 'encapsulate',
                    options: {
                        pre: "<poem>\n",
                        post: "\n</poem>"
                    }
                }
            }
        }
    } );
};

/* Check if view is in edit mode and that the required modules are available. Then, customize the toolbar … */
if ( [ 'edit', 'submit' ].indexOf( mw.config.get( 'wgAction' ) ) !== -1 ) {
	mw.loader.using( 'user.options' ).then( function () {
		// This can be the string "0" if the user disabled the preference ([[phab:T54542#555387]])
		if ( mw.user.options.get( 'usebetatoolbar' ) == 1 ) {
			$.when(
				mw.loader.using( 'ext.wikiEditor' ), $.ready
			).then( poemBtn );
		}
	} );
}