components/iron-overlay-behavior/iron-overlay-behavior.html

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@license
Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
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Code distributed by Google as part of the polymer project is also
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<link rel="import" href="../polymer/polymer.html">
<link rel="import" href="../iron-fit-behavior/iron-fit-behavior.html">
<link rel="import" href="../iron-resizable-behavior/iron-resizable-behavior.html">
<link rel="import" href="iron-overlay-manager.html">
<link rel="import" href="iron-focusables-helper.html">

<script>
(function() {
  'use strict';

  /** @polymerBehavior */
  Polymer.IronOverlayBehaviorImpl = {

    properties: {

      /**
       * True if the overlay is currently displayed.
       */
      opened: {
        observer: '_openedChanged',
        type: Boolean,
        value: false,
        notify: true
      },

      /**
       * True if the overlay was canceled when it was last closed.
       */
      canceled: {
        observer: '_canceledChanged',
        readOnly: true,
        type: Boolean,
        value: false
      },

      /**
       * Set to true to display a backdrop behind the overlay. It traps the focus
       * within the light DOM of the overlay.
       */
      withBackdrop: {
        observer: '_withBackdropChanged',
        type: Boolean
      },

      /**
       * Set to true to disable auto-focusing the overlay or child nodes with
       * the `autofocus` attribute` when the overlay is opened.
       */
      noAutoFocus: {
        type: Boolean,
        value: false
      },

      /**
       * Set to true to disable canceling the overlay with the ESC key.
       */
      noCancelOnEscKey: {
        type: Boolean,
        value: false
      },

      /**
       * Set to true to disable canceling the overlay by clicking outside it.
       */
      noCancelOnOutsideClick: {
        type: Boolean,
        value: false
      },

      /**
       * Contains the reason(s) this overlay was last closed (see `iron-overlay-closed`).
       * `IronOverlayBehavior` provides the `canceled` reason; implementers of the
       * behavior can provide other reasons in addition to `canceled`.
       */
      closingReason: {
        // was a getter before, but needs to be a property so other
        // behaviors can override this.
        type: Object
      },

      /**
       * Set to true to enable restoring of focus when overlay is closed.
       */
      restoreFocusOnClose: {
        type: Boolean,
        value: false
      },

      /**
       * Set to true to keep overlay always on top.
       */
      alwaysOnTop: {
        type: Boolean
      },

      /**
       * Shortcut to access to the overlay manager.
       * @private
       * @type {Polymer.IronOverlayManagerClass}
       */
      _manager: {
        type: Object,
        value: Polymer.IronOverlayManager
      },

      /**
       * The node being focused.
       * @type {?Node}
       */
      _focusedChild: {
        type: Object
      }

    },

    listeners: {
      'iron-resize': '_onIronResize'
    },

    /**
     * The backdrop element.
     * @type {Element}
     */
    get backdropElement() {
      return this._manager.backdropElement;
    },

    /**
     * Returns the node to give focus to.
     * @type {Node}
     */
    get _focusNode() {
      return this._focusedChild || Polymer.dom(this).querySelector('[autofocus]') || this;
    },

    /**
     * Array of nodes that can receive focus (overlay included), ordered by `tabindex`.
     * This is used to retrieve which is the first and last focusable nodes in order
     * to wrap the focus for overlays `with-backdrop`.
     *
     * If you know what is your content (specifically the first and last focusable children),
     * you can override this method to return only `[firstFocusable, lastFocusable];`
     * @type {Array<Node>}
     * @protected
     */
    get _focusableNodes() {
      return Polymer.IronFocusablesHelper.getTabbableNodes(this);
    },

    ready: function() {
      // Used to skip calls to notifyResize and refit while the overlay is animating.
      this.__isAnimating = false;
      // with-backdrop needs tabindex to be set in order to trap the focus.
      // If it is not set, IronOverlayBehavior will set it, and remove it if with-backdrop = false.
      this.__shouldRemoveTabIndex = false;
      // Used for wrapping the focus on TAB / Shift+TAB.
      this.__firstFocusableNode = this.__lastFocusableNode = null;
      // Used by __onNextAnimationFrame to cancel any previous callback.
      this.__raf = null;
      // Focused node before overlay gets opened. Can be restored on close.
      this.__restoreFocusNode = null;
      this._ensureSetup();
    },

    attached: function() {
      // Call _openedChanged here so that position can be computed correctly.
      if (this.opened) {
        this._openedChanged(this.opened);
      }
      this._observer = Polymer.dom(this).observeNodes(this._onNodesChange);
    },

    detached: function() {
      Polymer.dom(this).unobserveNodes(this._observer);
      this._observer = null;
      if (this.__raf) {
        window.cancelAnimationFrame(this.__raf);
        this.__raf = null;
      }
      this._manager.removeOverlay(this);
    },

    /**
     * Toggle the opened state of the overlay.
     */
    toggle: function() {
      this._setCanceled(false);
      this.opened = !this.opened;
    },

    /**
     * Open the overlay.
     */
    open: function() {
      this._setCanceled(false);
      this.opened = true;
    },

    /**
     * Close the overlay.
     */
    close: function() {
      this._setCanceled(false);
      this.opened = false;
    },

    /**
     * Cancels the overlay.
     * @param {Event=} event The original event
     */
    cancel: function(event) {
      var cancelEvent = this.fire('iron-overlay-canceled', event, {cancelable: true});
      if (cancelEvent.defaultPrevented) {
        return;
      }

      this._setCanceled(true);
      this.opened = false;
    },

    /**
     * Invalidates the cached tabbable nodes. To be called when any of the focusable
     * content changes (e.g. a button is disabled).
     */
    invalidateTabbables: function() {
      this.__firstFocusableNode = this.__lastFocusableNode = null;
    },

    _ensureSetup: function() {
      if (this._overlaySetup) {
        return;
      }
      this._overlaySetup = true;
      this.style.outline = 'none';
      this.style.display = 'none';
    },

    /**
     * Called when `opened` changes.
     * @param {boolean=} opened
     * @protected
     */
    _openedChanged: function(opened) {
      if (opened) {
        this.removeAttribute('aria-hidden');
      } else {
        this.setAttribute('aria-hidden', 'true');
      }

      // Defer any animation-related code on attached
      // (_openedChanged gets called again on attached).
      if (!this.isAttached) {
        return;
      }

      this.__isAnimating = true;

      // Use requestAnimationFrame for non-blocking rendering.
      this.__onNextAnimationFrame(this.__openedChanged);
    },

    _canceledChanged: function() {
      this.closingReason = this.closingReason || {};
      this.closingReason.canceled = this.canceled;
    },

    _withBackdropChanged: function() {
      // If tabindex is already set, no need to override it.
      if (this.withBackdrop && !this.hasAttribute('tabindex')) {
        this.setAttribute('tabindex', '-1');
        this.__shouldRemoveTabIndex = true;
      } else if (this.__shouldRemoveTabIndex) {
        this.removeAttribute('tabindex');
        this.__shouldRemoveTabIndex = false;
      }
      if (this.opened && this.isAttached) {
        this._manager.trackBackdrop();
      }
    },

    /**
     * tasks which must occur before opening; e.g. making the element visible.
     * @protected
     */
    _prepareRenderOpened: function() {
      // Store focused node.
      this.__restoreFocusNode = this._manager.deepActiveElement;

      // Needed to calculate the size of the overlay so that transitions on its size
      // will have the correct starting points.
      this._preparePositioning();
      this.refit();
      this._finishPositioning();

      // Safari will apply the focus to the autofocus element when displayed
      // for the first time, so we make sure to return the focus where it was.
      if (this.noAutoFocus && document.activeElement === this._focusNode) {
        this._focusNode.blur();
        this.__restoreFocusNode.focus();
      }
    },

    /**
     * Tasks which cause the overlay to actually open; typically play an animation.
     * @protected
     */
    _renderOpened: function() {
      this._finishRenderOpened();
    },

    /**
     * Tasks which cause the overlay to actually close; typically play an animation.
     * @protected
     */
    _renderClosed: function() {
      this._finishRenderClosed();
    },

    /**
     * Tasks to be performed at the end of open action. Will fire `iron-overlay-opened`.
     * @protected
     */
    _finishRenderOpened: function() {
      this.notifyResize();
      this.__isAnimating = false;

      this.fire('iron-overlay-opened');
    },

    /**
     * Tasks to be performed at the end of close action. Will fire `iron-overlay-closed`.
     * @protected
     */
    _finishRenderClosed: function() {
      // Hide the overlay.
      this.style.display = 'none';
      // Reset z-index only at the end of the animation.
      this.style.zIndex = '';
      this.notifyResize();
      this.__isAnimating = false;
      this.fire('iron-overlay-closed', this.closingReason);
    },

    _preparePositioning: function() {
      this.style.transition = this.style.webkitTransition = 'none';
      this.style.transform = this.style.webkitTransform = 'none';
      this.style.display = '';
    },

    _finishPositioning: function() {
      // First, make it invisible & reactivate animations.
      this.style.display = 'none';
      // Force reflow before re-enabling animations so that they don't start.
      // Set scrollTop to itself so that Closure Compiler doesn't remove this.
      this.scrollTop = this.scrollTop;
      this.style.transition = this.style.webkitTransition = '';
      this.style.transform = this.style.webkitTransform = '';
      // Now that animations are enabled, make it visible again
      this.style.display = '';
      // Force reflow, so that following animations are properly started.
      // Set scrollTop to itself so that Closure Compiler doesn't remove this.
      this.scrollTop = this.scrollTop;
    },

    /**
     * Applies focus according to the opened state.
     * @protected
     */
    _applyFocus: function() {
      if (this.opened) {
        if (!this.noAutoFocus) {
          this._focusNode.focus();
        }
      }
      else {
        this._focusNode.blur();
        this._focusedChild = null;
        // Restore focus.
        if (this.restoreFocusOnClose && this.__restoreFocusNode) {
          this.__restoreFocusNode.focus();
        }
        this.__restoreFocusNode = null;
        // If many overlays get closed at the same time, one of them would still
        // be the currentOverlay even if already closed, and would call _applyFocus
        // infinitely, so we check for this not to be the current overlay.
        var currentOverlay = this._manager.currentOverlay();
        if (currentOverlay && this !== currentOverlay) {
          currentOverlay._applyFocus();
        }
      }
    },

    /**
     * Cancels (closes) the overlay. Call when click happens outside the overlay.
     * @param {!Event} event
     * @protected
     */
    _onCaptureClick: function(event) {
      if (!this.noCancelOnOutsideClick) {
        this.cancel(event);
      }
    },

    /**
     * Keeps track of the focused child. If withBackdrop, traps focus within overlay.
     * @param {!Event} event
     * @protected
     */
    _onCaptureFocus: function (event) {
      if (!this.withBackdrop) {
        return;
      }
      var path = Polymer.dom(event).path;
      if (path.indexOf(this) === -1) {
        event.stopPropagation();
        this._applyFocus();
      } else {
        this._focusedChild = path[0];
      }
    },

    /**
     * Handles the ESC key event and cancels (closes) the overlay.
     * @param {!Event} event
     * @protected
     */
    _onCaptureEsc: function(event) {
      if (!this.noCancelOnEscKey) {
        this.cancel(event);
      }
    },

    /**
     * Handles TAB key events to track focus changes.
     * Will wrap focus for overlays withBackdrop.
     * @param {!Event} event
     * @protected
     */
    _onCaptureTab: function(event) {
      if (!this.withBackdrop) {
        return;
      }
      this.__ensureFirstLastFocusables();
      // TAB wraps from last to first focusable.
      // Shift + TAB wraps from first to last focusable.
      var shift = event.shiftKey;
      var nodeToCheck = shift ? this.__firstFocusableNode : this.__lastFocusableNode;
      var nodeToSet = shift ? this.__lastFocusableNode : this.__firstFocusableNode;
      var shouldWrap = false;
      if (nodeToCheck === nodeToSet) {
        // If nodeToCheck is the same as nodeToSet, it means we have an overlay
        // with 0 or 1 focusables; in either case we still need to trap the
        // focus within the overlay.
        shouldWrap = true;
      } else {
        // In dom=shadow, the manager will receive focus changes on the main
        // root but not the ones within other shadow roots, so we can't rely on
        // _focusedChild, but we should check the deepest active element.
        var focusedNode = this._manager.deepActiveElement;
        // If the active element is not the nodeToCheck but the overlay itself,
        // it means the focus is about to go outside the overlay, hence we
        // should prevent that (e.g. user opens the overlay and hit Shift+TAB).
        shouldWrap = (focusedNode === nodeToCheck || focusedNode === this);
      }

      if (shouldWrap) {
        // When the overlay contains the last focusable element of the document
        // and it's already focused, pressing TAB would move the focus outside
        // the document (e.g. to the browser search bar). Similarly, when the
        // overlay contains the first focusable element of the document and it's
        // already focused, pressing Shift+TAB would move the focus outside the
        // document (e.g. to the browser search bar).
        // In both cases, we would not receive a focus event, but only a blur.
        // In order to achieve focus wrapping, we prevent this TAB event and
        // force the focus. This will also prevent the focus to temporarily move
        // outside the overlay, which might cause scrolling.
        event.preventDefault();
        this._focusedChild = nodeToSet;
        this._applyFocus();
      }
    },

    /**
     * Refits if the overlay is opened and not animating.
     * @protected
     */
    _onIronResize: function() {
      if (this.opened && !this.__isAnimating) {
        this.__onNextAnimationFrame(this.refit);
      }
    },

    /**
     * Will call notifyResize if overlay is opened.
     * Can be overridden in order to avoid multiple observers on the same node.
     * @protected
     */
    _onNodesChange: function() {
      if (this.opened && !this.__isAnimating) {
        // It might have added focusable nodes, so invalidate cached values.
        this.invalidateTabbables();
        this.notifyResize();
      }
    },

    /**
     * Will set first and last focusable nodes if any of them is not set.
     * @private
     */
    __ensureFirstLastFocusables: function() {
      if (!this.__firstFocusableNode || !this.__lastFocusableNode) {
        var focusableNodes = this._focusableNodes;
        this.__firstFocusableNode = focusableNodes[0];
        this.__lastFocusableNode = focusableNodes[focusableNodes.length - 1];
      }
    },

    /**
     * Tasks executed when opened changes: prepare for the opening, move the
     * focus, update the manager, render opened/closed.
     * @private
     */
    __openedChanged: function() {
      if (this.opened) {
        // Make overlay visible, then add it to the manager.
        this._prepareRenderOpened();
        this._manager.addOverlay(this);
        // Move the focus to the child node with [autofocus].
        this._applyFocus();

        this._renderOpened();
      } else {
        // Remove overlay, then restore the focus before actually closing.
        this._manager.removeOverlay(this);
        this._applyFocus();

        this._renderClosed();
      }
    },

    /**
     * Executes a callback on the next animation frame, overriding any previous
     * callback awaiting for the next animation frame. e.g.
     * `__onNextAnimationFrame(callback1) && __onNextAnimationFrame(callback2)`;
     * `callback1` will never be invoked.
     * @param {!Function} callback Its `this` parameter is the overlay itself.
     * @private
     */
    __onNextAnimationFrame: function(callback) {
      if (this.__raf) {
        window.cancelAnimationFrame(this.__raf);
      }
      var self = this;
      this.__raf = window.requestAnimationFrame(function nextAnimationFrame() {
        self.__raf = null;
        callback.call(self);
      });
    }

  };

  /**
  Use `Polymer.IronOverlayBehavior` to implement an element that can be hidden or shown, and displays
  on top of other content. It includes an optional backdrop, and can be used to implement a variety
  of UI controls including dialogs and drop downs. Multiple overlays may be displayed at once.

  See the [demo source code](https://github.com/PolymerElements/iron-overlay-behavior/blob/master/demo/simple-overlay.html)
  for an example.

  ### Closing and canceling

  An overlay may be hidden by closing or canceling. The difference between close and cancel is user
  intent. Closing generally implies that the user acknowledged the content on the overlay. By default,
  it will cancel whenever the user taps outside it or presses the escape key. This behavior is
  configurable with the `no-cancel-on-esc-key` and the `no-cancel-on-outside-click` properties.
  `close()` should be called explicitly by the implementer when the user interacts with a control
  in the overlay element. When the dialog is canceled, the overlay fires an 'iron-overlay-canceled'
  event. Call `preventDefault` on this event to prevent the overlay from closing.

  ### Positioning

  By default the element is sized and positioned to fit and centered inside the window. You can
  position and size it manually using CSS. See `Polymer.IronFitBehavior`.

  ### Backdrop

  Set the `with-backdrop` attribute to display a backdrop behind the overlay. The backdrop is
  appended to `<body>` and is of type `<iron-overlay-backdrop>`. See its doc page for styling
  options.

  In addition, `with-backdrop` will wrap the focus within the content in the light DOM.
  Override the [`_focusableNodes` getter](#Polymer.IronOverlayBehavior:property-_focusableNodes)
  to achieve a different behavior.

  ### Limitations

  The element is styled to appear on top of other content by setting its `z-index` property. You
  must ensure no element has a stacking context with a higher `z-index` than its parent stacking
  context. You should place this element as a child of `<body>` whenever possible.

  @demo demo/index.html
  @polymerBehavior
  */
  Polymer.IronOverlayBehavior = [Polymer.IronFitBehavior, Polymer.IronResizableBehavior, Polymer.IronOverlayBehaviorImpl];

  /**
   * Fired after the overlay opens.
   * @event iron-overlay-opened
   */

  /**
   * Fired when the overlay is canceled, but before it is closed.
   * @event iron-overlay-canceled
   * @param {Event} event The closing of the overlay can be prevented
   * by calling `event.preventDefault()`. The `event.detail` is the original event that
   * originated the canceling (e.g. ESC keyboard event or click event outside the overlay).
   */

  /**
   * Fired after the overlay closes.
   * @event iron-overlay-closed
   * @param {Event} event The `event.detail` is the `closingReason` property
   * (contains `canceled`, whether the overlay was canceled).
   */

})();
</script>