How to make custom Hallo.js plugin/button call a js function (toggle a modal)

I need to have a custom button in the Hallo toolbar that will toggle a modal to open. I thought that it should be fairly simple to do, but there is not a lot of documentation for Hallo yet, and my knowledge of coffee script is not the best.

I've been able to create a basic plugin, by using the template given on their github page, but can not figure out how to have it call a js function to toggle the modal.

Any help is greatly appreciated. Thank you!

So this is what I ended up using... A lot of it was copied from the "Link" widget that came with hallo. It's very messy, and I wish I took the time to make it look better, but it works and I was in a hurry. I hope it may be useful for anyone else that needed the same customization. Just change the return value to be whatever function you want it to be.

(function(jQuery) {
return jQuery.widget("IKS.hallocustomimage", {
  options: {
    editable: null,
    uuid: "",
    link: true,
    image: true,
    dialogOpts: {
      autoOpen: false,
      width: 540,
      height: 95,
      modal: true,
      resizable: false,
      draggable: false,
      dialogClass: 'hallolink-dialog'
    },
    buttonCssClass: null
  },
  populateToolbar: function(toolbar) {
    var buttonize, buttonset, dialog, dialogSubmitCb, isEmptyLink, urlInput, widget,
      _this = this;
    widget = this;
    dialog = jQuery("<div id=\"" +  "\"><form action=\"#\" method=\"post\" class=\"linkForm\"><input class=\"url\" type=\"text\" name=\"url\"value=\"" + "\" /><input type=\"submit\" id=\"addlinkButton\" value=\"" + "\"/></form></div>");
    buttonset = jQuery("<span class=\"" + widget.widgetName + "\"></span>");
    buttonize = function(type) {
      var button, buttonHolder, id;
      id = "" + _this.options.uuid + "-" + type;
      buttonHolder = jQuery('<span></span>');
      buttonHolder.hallobutton({
        label: 'Image',
        icon: 'icon-picture',
        editable: _this.options.editable,
        command: null,
        queryState: false,
        uuid: _this.options.uuid,
        cssClass: _this.options.buttonCssClass
      });
      buttonset.append(buttonHolder);
      button = buttonHolder;
      button.on("click", function(event) {
        var button_selector, selectionParent;
        widget.options.editable.keepActivated(true);
        return jQuery(function(){$('#gallery').modal();});
      });
    };
    if (this.options.link) {
      buttonize("A");
    }
    if (this.options.link) {
      toolbar.append(buttonset);
      buttonset.hallobuttonset();
      return dialog.dialog(this.options.dialogOpts);
    }
  }
});})(jQuery);