@mdbootstrap/bootstrap-dark-mode/src/js/bootstrap/mdb-prefix/util/focustrap.js

Responsive Dark Mode theme built with Bootstrap 5 with Dark Mode toggle button that switches between dark and light themes.

/**
 * --------------------------------------------------------------------------
 * Bootstrap (v5.1.3): util/focustrap.js
 * Licensed under MIT (https://github.com/twbs/bootstrap/blob/main/LICENSE)
 * --------------------------------------------------------------------------
 */

import EventHandler from '../dom/event-handler';
import SelectorEngine from '../dom/selector-engine';
import { typeCheckConfig } from './index';

const Default = {
  trapElement: null, // The element to trap focus inside of
  autofocus: true,
};

const DefaultType = {
  trapElement: 'element',
  autofocus: 'boolean',
};

const NAME = 'focustrap';
const DATA_KEY = 'bs.focustrap';
const EVENT_KEY = `.${DATA_KEY}`;
const EVENT_FOCUSIN = `focusin${EVENT_KEY}`;
const EVENT_KEYDOWN_TAB = `keydown.tab${EVENT_KEY}`;

const TAB_KEY = 'Tab';
const TAB_NAV_FORWARD = 'forward';
const TAB_NAV_BACKWARD = 'backward';

class FocusTrap {
  constructor(config) {
    this._config = this._getConfig(config);
    this._isActive = false;
    this._lastTabNavDirection = null;
  }

  activate() {
    const { trapElement, autofocus } = this._config;

    if (this._isActive) {
      return;
    }

    if (autofocus) {
      trapElement.focus();
    }

    EventHandler.off(document, EVENT_KEY); // guard against infinite focus loop
    EventHandler.on(document, EVENT_FOCUSIN, (event) => this._handleFocusin(event));
    EventHandler.on(document, EVENT_KEYDOWN_TAB, (event) => this._handleKeydown(event));

    this._isActive = true;
  }

  deactivate() {
    if (!this._isActive) {
      return;
    }

    this._isActive = false;
    EventHandler.off(document, EVENT_KEY);
  }

  // Private

  _handleFocusin(event) {
    const { target } = event;
    const { trapElement } = this._config;

    if (target === document || target === trapElement || trapElement.contains(target)) {
      return;
    }

    const elements = SelectorEngine.focusableChildren(trapElement);

    if (elements.length === 0) {
      trapElement.focus();
    } else if (this._lastTabNavDirection === TAB_NAV_BACKWARD) {
      elements[elements.length - 1].focus();
    } else {
      elements[0].focus();
    }
  }

  _handleKeydown(event) {
    if (event.key !== TAB_KEY) {
      return;
    }

    this._lastTabNavDirection = event.shiftKey ? TAB_NAV_BACKWARD : TAB_NAV_FORWARD;
  }

  _getConfig(config) {
    config = {
      ...Default,
      ...(typeof config === 'object' ? config : {}),
    };
    typeCheckConfig(NAME, config, DefaultType);
    return config;
  }
}

export default FocusTrap;