_shopmsg('overlay.render', pluginId);

You may want to manually show an overlay plugin (e.g. Modal, Flyout, or Page Takover) after some custom conditions are met on your site. You will need the pluginId (a number) of the overlay you wish to render, then simply call _shopmsg('overlay.render', pluginId) against your plugin;

// example of waiting for some promise to be fulfilled to render a plugin
let showPlugin = new Promise(...);
showPlugin.then(() => {
  // render overlay with id=36534
  _shopmsg('overlay.render', 36534);