Frontend Pages and Resolvers

As explained in the Routes and Content documentation, we can use Mithril's routing system to show different components for different routes. Mithril allows you to use any component you like, even a Modal or Alert, but we recommend sticking to component classes that inherit the Page component.

We provide flarum/common/components/Page as a base class for pages in both the admin and forum frontends. It has a few benefits:

• Automatically updates app.current and app.previous PageState when switching from one route to another.
• Automatically closes the modal and drawer when switching from one route to another.
• Applies this.bodyClass (if defined) to the '#app' HTML element when the page renders.
• It's also good for consistency's sake to use a common base class for all pages.
• If the page's scrollTopOnCreate attribute is set to false in oninit, the page won't be scrolled to the top when changed.
• If the page's useBrowserScrollRestoration is set to false in oninit, the browser's automatic scroll restoration won't be used on that page.

Page components work just like any other inherited component. For a (very simple) example:

import Page from 'flarum/common/components/Page';




export default class CustomPage extends Page {
  view() {
    return <p>Hello!</p>
  }
}

Flarum uses a setting to determine which page should be the homepage: this gives admins flexibility to customize their communities. To add your custom page to the homepage options in Admin, you'll need to extend the BasicsPage.homePageItems method with your page's path.

An example from the Tags extension:

import { extend } from 'flarum/common/extend';
import BasicsPage from 'flarum/common/components/BasicsPage';


export default function() {
  extend(BasicsPage.prototype, 'homePageItems', items => {
    items.add('tags', {
      path: '/tags',
      label: app.translator.trans('flarum-tags.admin.basics.tags_label')
    });
  });
}

To learn how to set up a path/route for your custom page, see the relevant documentation.

Often, you'll want some custom text to appear in the browser tab's title for your page. For instance, a tags page might want to show "Tags - FORUM NAME", or a discussion page might want to show the title of the discussion.

To do this, your page should include calls to app.setTitle() and app.setTitleCount() in its oncreate lifecycle hook (or when data is loaded, if it pulls in data from the API).

For example:

import Page from 'flarum/common/components/Page';




export default class CustomPage extends Page {
  oncreate(vnode) {
    super.oncreate(vnode);


    app.setTitle("Cool Page");
    app.setTitleCount(0);
  }


  view() {
    // ...
  }
}


export default class CustomPageLoadsData extends Page {
  oninit(vnode) {
    super.oninit(vnode);


    app.store.find("users", 1).then(user => {
      app.setTitle(user.displayName());
      app.setTitleCount(0);
    })
  }


  view() {
    // ...
  }
}

Please note that if your page is set as the homepage, app.setTitle() will clear the title for simplicity. It should still be called though, to prevent titles from previous pages from carrying over.

Sometimes, we want to get information about the page we're currently on, or the page we've just come from. To allow this, Flarum creates (and stores) instances of PageState as app.current and app.previous. These store:

• The component class being used for the page
• A collection of data that each page sets about itself. The current route name is always included.

Data can be set to, and retrieved from, Page State using:

app.current.set(KEY, DATA);
app.current.get(KEY);

For example, this is how the Discussion Page makes its PostStreamState instance globally available.

You can also check the type and data of a page using PostStreamState's matches method. For instance, if we want to know if we are currently on a discussion page:

import IndexPage from 'flarum/forum/components/DiscussionPage';
import DiscussionPage from 'flarum/forum/components/DiscussionPage';


// To just check page type
app.current.matches(DiscussionPage);


// To check page type and some data
app.current.matches(IndexPage, {routeName: 'following'});

See the Admin Dashboard documentation for more information on tools specifically available to admin pages (and how to override the admin page for your extension).

Advanced use cases can take advantage of Mithril's route resolver system. Flarum actually already wraps all its components in the flarum/common/resolvers/DefaultResolver resolver. This has the following benefits:

• It passes a routeName attr to the current page, which then provides it to PageState
• It assigns a key to the top level page component. When the route changes, if the top level component's key has changed, it will be completely rerendered (by default, Mithril does not rerender components when switching from one page to another if both are handled by the same component).

There are actually 3 ways to set the component / route resolver when registering a route:

• the resolver key can be used to provide an instance of a route resolver. This instance should define which component should be used, and hardcode the route name to be passed into it. This instance will be used without any modifications by Flarum.
• The resolverClass key AND component key can be used to provide a class that will be used to instantiate a route resolver, to be used instead of Flarum's default one, as well as the component to use. Its constructor should take 2 arguments: (component, routeName).
• The component key can be used alone to provide a component. This will result in the default behavior.

For example:

// See above for a custom page example
import CustomPage from './components/CustomPage';
// See below for a custom resolver example
import CustomPageResolver from './resolvers/CustomPageResolver';


// Use a route resolver instance
app.routes['resolverInstance'] = {path: '/custom/path/1', resolver: {
  onmatch: function(args) {
    if (!app.session.user) return m.route.SKIP;


    return CustomPage;
  }
}};


// Use a custom route resolver class
app.routes['resolverClass'] = {path: '/custom/path/2', resolverClass: CustomPageResolver, component: CustomPage};


// Use the default resolver class (`flarum/common/resolvers/DefaultResolver`)
app.routes['resolverClass'] = {path: '/custom/path/2', component: CustomPage};

We strongly encourage custom route resolvers to extend flarum/common/resolvers/DefaultResolver. For example, Flarum's flarum/forum/resolvers/DiscussionPageResolver assigns the same key to all links to the same discussion (regardless of the current post), and triggers scrolling when using m.route.set to go from one post to another on the same discussion page:

import DefaultResolver from '../../common/resolvers/DefaultResolver';


/**
 * This isn't exported as it is a temporary measure.
 * A more robust system will be implemented alongside UTF-8 support in beta 15.
 */
function getDiscussionIdFromSlug(slug: string | undefined) {
  if (!slug) return;
  return slug.split('-')[0];
}


/**
 * A custom route resolver for DiscussionPage that generates the same key to all posts
 * on the same discussion. It triggers a scroll when going from one post to another
 * in the same discussion.
 */
export default class DiscussionPageResolver extends DefaultResolver {
  static scrollToPostNumber: number | null = null;


  makeKey() {
    const params = { ...m.route.param() };
    if ('near' in params) {
      delete params.near;
    }
    params.id = getDiscussionIdFromSlug(params.id);
    return this.routeName.replace('.near', '') + JSON.stringify(params);
  }


  onmatch(args, requestedPath, route) {
    if (route.includes('/d/:id') && getDiscussionIdFromSlug(args.id) === getDiscussionIdFromSlug(m.route.param('id'))) {
      DiscussionPageResolver.scrollToPostNumber = parseInt(args.near);
    }


    return super.onmatch(args, requestedPath, route);
  }


  render(vnode) {
    if (DiscussionPageResolver.scrollToPostNumber !== null) {
      const number = DiscussionPageResolver.scrollToPostNumber;
      // Scroll after a timeout to avoid clashes with the render.
      setTimeout(() => app.current.get('stream').goToNumber(number));
      DiscussionPageResolver.scrollToPostNumber = null;
    }


    return super.render(vnode);
  }
}