chrome/browser/resources/bookmarks/dialog_focus_manager.js

// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

cr.define('bookmarks', function() {
  /**
   * Manages focus restoration for modal dialogs. After the final dialog in a
   * stack is closed, restores focus to the element which was focused when the
   * first dialog was opened.
   */
  class DialogFocusManager {
    constructor() {
      /** @private {HTMLElement} */
      this.previousFocusElement_ = null;

      /** @private {Set<HTMLDialogElement>} */
      this.dialogs_ = new Set();
    }

    /**
     * @param {HTMLDialogElement} dialog
     * @param {function()=} showFn
     */
    showDialog(dialog, showFn) {
      if (!showFn) {
        showFn = function() {
          dialog.showModal();
        };
      }

      // Update the focus if there are no open dialogs or if this is the only
      // dialog and it's getting reshown.
      if (!this.dialogs_.size ||
          (this.dialogs_.has(dialog) && this.dialogs_.size == 1)) {
        this.updatePreviousFocus_();
      }

      if (!this.dialogs_.has(dialog)) {
        dialog.addEventListener('close', this.getCloseListener_(dialog));
        this.dialogs_.add(dialog);
      }

      showFn();
    }

    /**
     * @return {boolean} True if the document currently has an open dialog.
     */
    hasOpenDialog() {
      return this.dialogs_.size > 0;
    }

    /**
     * Clears the stored focus element, so that focus does not restore when all
     * dialogs are closed.
     */
    clearFocus() {
      this.previousFocusElement_ = null;
    }

    /** @private */
    updatePreviousFocus_() {
      this.previousFocusElement_ = this.getFocusedElement_();
    }

    /**
     * @return {HTMLElement}
     * @private
     */
    getFocusedElement_() {
      let focus = document.activeElement;
      while (focus.root && focus.root.activeElement) {
        focus = focus.root.activeElement;
      }

      return focus;
    }

    /**
     * @param {HTMLDialogElement} dialog
     * @return {function(Event)}
     * @private
     */
    getCloseListener_(dialog) {
      const closeListener = (e) => {
        // If the dialog is open, then it got reshown immediately and we
        // shouldn't clear it until it is closed again.
        if (dialog.open) {
          return;
        }

        assert(this.dialogs_.delete(dialog));
        // Focus the originally focused element if there are no more dialogs.
        if (!this.hasOpenDialog() && this.previousFocusElement_) {
          this.previousFocusElement_.focus();
        }

        dialog.removeEventListener('close', closeListener);
      };

      return closeListener;
    }
  }

  cr.addSingletonGetter(DialogFocusManager);

  return {
    DialogFocusManager: DialogFocusManager,
  };
});