main.js

(function(){
    var ChannelCollapse = {
        addToolbarItem: function() {
            if(document.querySelectorAll('.show-channels-button').length == 0) {
                var newToolbarItem = document.createElement('button');
                newToolbarItem.type = 'button';
                newToolbarItem.classList.add('show-channels-button');
                newToolbarItem.classList.add('active');
                newToolbarItem.innerHTML = '<span style="display: block; color: #fefefe; -webkit-transform: scale(2.0, 1.0); -moz-transform:scale(2.0, 1.0); -ms-transform:scale(2.0, 1.0); -o-transform:scale(2.0, 1.0); transform: scale(6,1); width: 0; height: 5px; text-align: center; position: absolute; top: 1px; left: 0;">-</span><span style="display: block; color: #fefefe; -webkit-transform: scale(2.0, 1.0); -moz-transform:scale(2.0, 1.0); -ms-transform:scale(2.0, 1.0); -o-transform:scale(2.0, 1.0); transform: scale(6,1); width: 0; height: 5px; position: absolute; top: 6px; left: 0;">-</span><span style="display: block; color: #fefefe; -webkit-transform: scale(2.0, 1.0); -moz-transform:scale(2.0, 1.0); -ms-transform:scale(2.0, 1.0); -o-transform:scale(2.0, 1.0); transform: scale(6,1); width: 0; height: 5px; position: absolute; top: 11px; left: 0;">-</span>';

                document.querySelector('.header-toolbar').insertBefore(newToolbarItem,document.querySelector('.header-toolbar div.separator'));
                
                document.querySelector('.show-channels-button').addEventListener('click',function(e){
                    if(this.classList.contains('active')) {
                        document.querySelector('.channels-wrap').style.display = 'none';
                        this.classList.toggle('active');
                    } else {
                        document.querySelector('.channels-wrap').style.display = 'flex';
                        this.classList.toggle('active');
                    }
                });
            }
        },
        addEventListeners: function(){
            var guilds = document.querySelectorAll('.guild');
            for(var i = 0;i < guilds.length; ++i) {
                guilds[i].addEventListener('click',function(){
                    window.setTimeout(function(){
                        console.log("Added event listener");
                        ChannelCollapse.addToolbarItem();
                    },1);
                });
            }
        }
    };

    ChannelCollapse.addToolbarItem();
    ChannelCollapse.addEventListeners();
})();