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Overlays: Features

The overlay system allows to create different types of overlays like dialogs, toasts, tooltips, dropdown, etc. It's designed to be highly flexible, while still delivering sensible defaults. On top of this, the system was built having accessibility in mind.

For a detailed rationale, please consult Rationale.

OverlayController

OverlayController is the single class we instantiate whenever creating an overlay instance. Based on provided config, it will handle:

  • DOM position (local vs global)
  • positioning logic
  • accessibility
  • interaction patterns

and has the following public functions:

  • show(), to show the overlay
  • hide(), to hide the overlay
  • toggle(), to toggle between show and hide

All overlays contain an invokerNode and a contentNode

  • contentNode, the toggleable content of the overlay.
  • invokerNode, the element toggles the visibility of the content. For local overlays, this is the relative element the content is positioned to

Make sure you pass a DOM-connected contentNode, an offline rendered (e.g. with just document.createElement or renderLitAsNode) will not work, because then we cannot determine the renderTarget to render the content to.

For DOM position, local refers to overlays where the content is positioned next to the invokers they are related to, DOM-wise. Global refers to overlays where the content is positioned in a global root node at the bottom of <body>.

Configuration

Overlays can be configured in many ways to suit your needs. We go in-depth into each option in the Overlay System - Configuration chapter.

We also export a few preset configuration objects.

  • withModalDialogConfig
  • withDropdownConfig
  • withBottomSheetConfig

You import these using ES Modules, and then simply call them inside your OverlayController instantiation:

const ctrl = new OverlayController({
  ...withModalDialogConfig(),
  invokerNode,
  contentNode,
});

or in your Web Component with OverlayMixin, make sure you override these methods to:

  • Define configuration
  • Handle setting up event listeners of toggling the opened state of your overlay
  • Handle the tearing down of those event listeners
  • Define a template which includes:
    • invoker slot for your user to provide the invoker node (the element that invokes the overlay content)
    • content slot for your user to provide the content that shows when the overlay is opened, make sure to put it inside a div with id overlay-content-node-wrapper which is necessary for positioning logic to work properly.
_defineOverlayConfig() {
  return {
    ...withModalDialogConfig
  };
}

_setupOpenCloseListeners() {
  super._setupOpenCloseListeners();
  this.__toggle = () => {
    this.opened = !this.opened;
  };

  if (this._overlayInvokerNode) {
    this._overlayInvokerNode.addEventListener('click', this.__toggle);
  }
}

_teardownOpenCloseListeners() {
  super._teardownOpenCloseListeners();

  if (this._overlayInvokerNode) {
    this._overlayInvokerNode.removeEventListener('click', this.__toggle);
  }
}

render() {
  return html`
    <slot name="invoker"></slot>
    <div id="overlay-content-node-wrapper">
      <slot name="content"></slot>
    </div>
  `;
}

or declaratively in your template with the .config property

<demo-overlay-system .config=$>
  <button slot="invoker">Click me to open the overlay!</button>
  <div slot="content" class="demo-overlay">
    Hello! You can close this notification here:
    <button
      @click=${e => e.target.dispatchEvent(new Event('close-overlay', { bubbles: true }))}
    >
      тип
    </button>
  </div>
</demo-overlay-system>

Backdrop

There are multiple ways to pass a backdrop node for your overlay.

The easiest way is declarative. This can be achieved by adding a <slot name="backdrop"> to your render method. The component user can then insert a backdrop slottable declaratively:

You can also pass a backdropNode imperatively to the OverlayConfig. Either use hasBackdrop: true, which will spawn a default backdropNode. For more control, pass a backdropNode yourself, e.g. a webcomponent so you can easily encapsulate styles.

Backdrop animation

By default our overlay system comes with a backdrop animation. This will add global-overlays__backdrop--animation-in and global-overlays__backdrop--animation-out classes to your backdrop node. If you have placementMode: 'local' it will replace those global strings in the CSS classes with local.

It expects from you that you act on these classes in your CSS with an animation. For example if you have your own backdrop webcomponent (to encapsulate styles):

:host(.local-overlays__backdrop--animation-in) {
  animation: local-overlays-backdrop-fade-in 300ms;
}

:host(.local-overlays__backdrop--animation-out) {
  animation: local-overlays-backdrop-fade-out 300ms;
  opacity: 0;
}

@keyframes local-overlays-backdrop-fade-in {
  from {
    opacity: 0;
  }
}

@keyframes local-overlays-backdrop-fade-out {
  from {
    opacity: 0.3;
  }
}

Under the hood, the OverlayController listens to animationend event, only then it will remove the animation-out/animation-in classes.

If you don't intend on having a backdrop animation at all, as a subclasser you should override transitionHide and transitionShow OverlayMixin methods. Otherwise the hide will await an animationend event that will never happen.

Responsive switching

Currently we support switching between overlay configurations. Keep in mind however that we do not yet support switching between overlay configurations while the content is shown. If you try, it will close the content if it is open, and the user will need to re-open. Will be supported in the near future.

This can be done declaratively as shown below. Drag the viewport under 600px and open the overlay to see the withBottomSheetConfig applied.

Alternative ways to do it is by setting the event listener manually on the OverlayController instance.

myOverlayCtrl.addEventListener('before-show', () => {
  if (window.innerWidth >= 600) {
    ctrl.updateConfig(withModalDialogConfig());
  } else {
    ctrl.updateConfig(withBottomSheetConfig());
  }
});

Or inside of a Web Component that uses the OverlayMixin, by overriding protected method _defineOverlay, where we can access the OverlayController instance and use the updateConfig method on the controller:

_defineOverlay({ invokerNode, contentNode }) {

  // initial
  const ctrl = new OverlayController({
    ...withBottomSheetConfig(),
    hidesOnOutsideClick: true,
    invokerNode,
    contentNode,
  });

  // responsive
  ctrl.addEventListener('before-show', () => {
    if (window.innerWidth >= 600) {
      ctrl.updateConfig(withModalDialogConfig());
    } else {
      ctrl.updateConfig(withBottomSheetConfig());
    }
  });

  return ctrl;

Below is another demo where you can toggle between configurations using buttons.

Opened state

For any overlay that implements the OverlayMixin, there is a Boolean property opened that reflects whether the overlay content is displayed or not.

You can also listen to the event opened-changed which is fired whenever opened is toggled. This can be useful e.g. if somewhere in your application you need to rely on this "state".

Intercepting open/close

It is possible to intercept the open/close process by calling .preventDefault() on the before-close or before-open events.

OverlayMixin

OverlayMixin is a mixin anyone can use to create a Web Component which has a content node (slot="content") and invoker node (slot="invoker").

Under the hood, the OverlayMixin will instantiate an OverlayController with these nodes.

By default, there are only a few OverlayMixin methods you need to override to create a working Web Component using an overlay:

  • render, the template needs to include a <slot name="invoker"> and <slot name="content"> inside a div with id overlay-content-node-wrapper (for positioning).
  • _defineOverlayConfig, in this protected method, return an object that contains the default configuration for your Web Component's overlay. See configuration section of OverlayController.
  • _setupOpenCloseListeners, use this lifecycle hook to setup the open and close event listeners on your _overlayInvokerNode.
  • _teardownOpenCloseListeners, use this lifecycle hook to ensure that the listeners are removed when the OverlayController is tearing down. For example when the Web Component is disconnected from the DOM.
import { LitElement } from '@lion/core';
import { OverlayMixin } from '@lion/overlays';

class MyOverlayWC extends OverlayMixin(LitElement) {
  _defineOverlayConfig() {
    return {
      placementMode: 'global',
      hasBackdrop: true,
    };
  }

  _setupOpenCloseListeners() {
    super._setupOpenCloseListeners();
    this.__toggle = () => {
      // opened is the public boolean property to use in the WC for opening/closing
      this.opened = !this.opened;
    };

    // Always guard this, because your user may toggle the opened state through something else (e.g. event) and not an invoker node.
    if (this._overlayInvokerNode) {
      this._overlayInvokerNode.addEventListener('click', this.__toggle);
    }
  }

  _teardownOpenCloseListeners() {
    super._teardownOpenCloseListeners();

    if (this._overlayInvokerNode) {
      this._overlayInvokerNode.removeEventListener('click', this.__toggle);
    }
  }

  render() {
    return html`
      <slot name="invoker"></slot>
      <div id="overlay-content-node-wrapper">
        <slot name="content"></slot>
      </div>
    `;
  }
}

OverlaysManager

The OverlaysManager is a global registry keeping track of all different types of overlays. The need for a global housekeeping mainly arises when multiple overlays are opened simultaneously.

For example, you may have a modal dialog that opens another modal dialog. The second dialog needs to block the first. When the second dialog is closed, the first one is available again.

The overlay manager keeps track of all registered overlays and controls which one to show.

Below an example is shown with the isBlocking option, which makes use of the OverlaysManager's capabilities.

Local Backdrop

We provide a possibility to add a backdrop to a locally placed overlay. You can pass your backdropNode as a configuration parameter and control its styling reacting upon OverlayController events. Here is the example below

Nested Overlays

Overlays can be nested, as the demo below shows. It's also possible to compose a nested construction by moving around dom nodes.

Local overlay with an arrow

To add an arrow to the localOverlay you can add ArrowMixin to your component. And add the arrowPopperConfig to the _defineOverlayConfig.