How to add Tooltip and a button in Composer Toolbar

Can anyone help me regarding below the onclick is frontend function not backend so its not showing in the source and when i click on it nothing happens, So how can I add that onclick in that button, I mean like button <button onclick= "imageGUI()">Content</button>

import { extend } from 'flarum/common/extend';
import app from 'flarum/common/app';
import TextEditor from 'flarum/common/components/TextEditor';

app.initializers.add('ramesh-dada/flarum-gui-image-and-link', () => {
    extend(TextEditor.prototype, 'toolbarItems', function (items) {
        items.add(
            'ramesh-dada-premium-imagegui',
            
            m(
                'Tooltip',
                {
                text: app.translator.trans('ramesh.imageGUI'),
                },
                [
                m('button',
                {
                    type: 'buton',
                    class: 'Button Button--icon Button--link hasIcon GuiImage',
                    title: app.translator.trans('ramesh.imageGUI'),
                    onclick: 'imageGUI()'
                }),
                ],
                [ m('i', { class: 'fas fa-image' }),],
                [ m('span', { class: 'Button-label' }, app.translator.trans('ramesh.imageGUI')), ]
            ),

            4
        );
    });

    extend(TextEditor.prototype, 'toolbarItems', function (items) {
        items.add(
            'ramesh-dada-premium-linkgui',
            m(
                'Tooltip',
                {
                text: app.translator.trans('ramesh.linkGUI'),
                },
                [
                m('button',
                {
                    type: 'buton',
                    class: 'Button Button--icon Button--link hasIcon GuiImage',
                    title: app.translator.trans('ramesh.linkGUI'),
                    onclick: 'linkGUI()'
                }),
                ],
                [ m('i', { class: 'fas fa-link' }),],
                [ m('span', { class: 'Button-label' }, app.translator.trans('ramesh.linkGUI')), ]
            ),
            
            5
        );
    });
});

and also Tooltip is showing as html
which is ultra bad
please help me regarding this

Justoverclock THANKS For your reply But I want to add a button in a composer tray in which bold italic and other icons appear

Justoverclock I done all the things I just want to add a tooltip which doesn't seems to be working!!!!