purify.js

import * as TAGS from './tags.js';
import * as ATTRS from './attrs.js';
import * as EXPRESSIONS from './regexp.js';
import {
  addToSet,
  clone,
  freeze,
  arrayForEach,
  arrayPop,
  arrayPush,
  stringMatch,
  stringReplace,
  stringToLowerCase,
  stringIndexOf,
  stringTrim,
  regExpTest,
  typeErrorCreate,
  lookupGetter,
} from './utils.js';

const getGlobal = () => (typeof window === 'undefined' ? null : window);

/**
 * Creates a no-op policy for internal use only.
 * Don't export this function outside this module!
 * @param {?TrustedTypePolicyFactory} trustedTypes The policy factory.
 * @param {Document} document The document object (to determine policy name suffix)
 * @return {?TrustedTypePolicy} The policy created (or null, if Trusted Types
 * are not supported).
 */
const _createTrustedTypesPolicy = function (trustedTypes, document) {
  if (
    typeof trustedTypes !== 'object' ||
    typeof trustedTypes.createPolicy !== 'function'
  ) {
    return null;
  }

  // Allow the callers to control the unique policy name
  // by adding a data-tt-policy-suffix to the script element with the DOMPurify.
  // Policy creation with duplicate names throws in Trusted Types.
  let suffix = null;
  const ATTR_NAME = 'data-tt-policy-suffix';
  if (
    document.currentScript &&
    document.currentScript.hasAttribute(ATTR_NAME)
  ) {
    suffix = document.currentScript.getAttribute(ATTR_NAME);
  }

  const policyName = 'dompurify' + (suffix ? '#' + suffix : '');

  try {
    return trustedTypes.createPolicy(policyName, {
      createHTML(html) {
        return html;
      },
    });
  } catch (_) {
    // Policy creation failed (most likely another DOMPurify script has
    // already run). Skip creating the policy, as this will only cause errors
    // if TT are enforced.
    console.warn(
      'TrustedTypes policy ' + policyName + ' could not be created.'
    );
    return null;
  }
};

function createDOMPurify(window = getGlobal()) {
  const DOMPurify = (root) => createDOMPurify(root);

  /**
   * Version label, exposed for easier checks
   * if DOMPurify is up to date or not
   */
  DOMPurify.version = VERSION;

  /**
   * Array of elements that DOMPurify removed during sanitation.
   * Empty if nothing was removed.
   */
  DOMPurify.removed = [];

  if (!window || !window.document || window.document.nodeType !== 9) {
    // Not running in a browser, provide a factory function
    // so that you can pass your own Window
    DOMPurify.isSupported = false;

    return DOMPurify;
  }

  const originalDocument = window.document;

  let { document } = window;
  const {
    DocumentFragment,
    HTMLTemplateElement,
    Node,
    Element,
    NodeFilter,
    NamedNodeMap = window.NamedNodeMap || window.MozNamedAttrMap,
    HTMLFormElement,
    DOMParser,
    trustedTypes,
  } = window;

  const ElementPrototype = Element.prototype;

  const cloneNode = lookupGetter(ElementPrototype, 'cloneNode');
  const getNextSibling = lookupGetter(ElementPrototype, 'nextSibling');
  const getChildNodes = lookupGetter(ElementPrototype, 'childNodes');
  const getParentNode = lookupGetter(ElementPrototype, 'parentNode');

  // As per issue #47, the web-components registry is inherited by a
  // new document created via createHTMLDocument. As per the spec
  // (http://w3c.github.io/webcomponents/spec/custom/#creating-and-passing-registries)
  // a new empty registry is used when creating a template contents owner
  // document, so we use that as our parent document to ensure nothing
  // is inherited.
  if (typeof HTMLTemplateElement === 'function') {
    const template = document.createElement('template');
    if (template.content && template.content.ownerDocument) {
      document = template.content.ownerDocument;
    }
  }

  const trustedTypesPolicy = _createTrustedTypesPolicy(
    trustedTypes,
    originalDocument
  );
  const emptyHTML = trustedTypesPolicy ? trustedTypesPolicy.createHTML('') : '';

  const {
    implementation,
    createNodeIterator,
    createDocumentFragment,
    getElementsByTagName,
  } = document;
  const { importNode } = originalDocument;

  let documentMode = {};
  try {
    documentMode = clone(document).documentMode ? document.documentMode : {};
  } catch (_) {}

  let hooks = {};

  /**
   * Expose whether this browser supports running the full DOMPurify.
   */
  DOMPurify.isSupported =
    typeof getParentNode === 'function' &&
    implementation &&
    typeof implementation.createHTMLDocument !== 'undefined' &&
    documentMode !== 9;

  const {
    MUSTACHE_EXPR,
    ERB_EXPR,
    DATA_ATTR,
    ARIA_ATTR,
    IS_SCRIPT_OR_DATA,
    ATTR_WHITESPACE,
  } = EXPRESSIONS;

  let { IS_ALLOWED_URI } = EXPRESSIONS;

  /**
   * We consider the elements and attributes below to be safe. Ideally
   * don't add any new ones but feel free to remove unwanted ones.
   */

  /* allowed element names */
  let ALLOWED_TAGS = null;
  const DEFAULT_ALLOWED_TAGS = addToSet({}, [
    ...TAGS.html,
    ...TAGS.svg,
    ...TAGS.svgFilters,
    ...TAGS.mathMl,
    ...TAGS.text,
  ]);

  /* Allowed attribute names */
  let ALLOWED_ATTR = null;
  const DEFAULT_ALLOWED_ATTR = addToSet({}, [
    ...ATTRS.html,
    ...ATTRS.svg,
    ...ATTRS.mathMl,
    ...ATTRS.xml,
  ]);

  /*
   * Configure how DOMPUrify should handle custom elements and their attributes as well as customized built-in elements.
   * @property {RegExp|Function|null} tagNameCheck one of [null, regexPattern, predicate]. Default: `null` (disallow any custom elements)
   * @property {RegExp|Function|null} attributeNameCheck one of [null, regexPattern, predicate]. Default: `null` (disallow any attributes not on the allow list)
   * @property {boolean} allowCustomizedBuiltInElements allow custom elements derived from built-ins if they pass CUSTOM_ELEMENT_HANDLING.tagNameCheck. Default: `false`.
   */
  const CUSTOM_ELEMENT_HANDLING = Object.seal(
    Object.create(null, {
      tagNameCheck: {
        writable: true,
        configurable: false,
        enumerable: true,
        value: null,
      },
      attributeNameCheck: {
        writable: true,
        configurable: false,
        enumerable: true,
        value: null,
      },
      allowCustomizedBuiltInElements: {
        writable: true,
        configurable: false,
        enumerable: true,
        value: false,
      },
    })
  );

  /* Explicitly forbidden tags (overrides ALLOWED_TAGS/ADD_TAGS) */
  let FORBID_TAGS = null;

  /* Explicitly forbidden attributes (overrides ALLOWED_ATTR/ADD_ATTR) */
  let FORBID_ATTR = null;

  /* Decide if ARIA attributes are okay */
  let ALLOW_ARIA_ATTR = true;

  /* Decide if custom data attributes are okay */
  let ALLOW_DATA_ATTR = true;

  /* Decide if unknown protocols are okay */
  let ALLOW_UNKNOWN_PROTOCOLS = false;

  /* Output should be safe for common template engines.
   * This means, DOMPurify removes data attributes, mustaches and ERB
   */
  let SAFE_FOR_TEMPLATES = false;

  /* Decide if document with <html>... should be returned */
  let WHOLE_DOCUMENT = false;

  /* Track whether config is already set on this instance of DOMPurify. */
  let SET_CONFIG = false;

  /* Decide if all elements (e.g. style, script) must be children of
   * document.body. By default, browsers might move them to document.head */
  let FORCE_BODY = false;

  /* Decide if a DOM `HTMLBodyElement` should be returned, instead of a html
   * string (or a TrustedHTML object if Trusted Types are supported).
   * If `WHOLE_DOCUMENT` is enabled a `HTMLHtmlElement` will be returned instead
   */
  let RETURN_DOM = false;

  /* Decide if a DOM `DocumentFragment` should be returned, instead of a html
   * string  (or a TrustedHTML object if Trusted Types are supported) */
  let RETURN_DOM_FRAGMENT = false;

  /* Try to return a Trusted Type object instead of a string, return a string in
   * case Trusted Types are not supported  */
  let RETURN_TRUSTED_TYPE = false;

  /* Output should be free from DOM clobbering attacks? */
  let SANITIZE_DOM = true;

  /* Keep element content when removing element? */
  let KEEP_CONTENT = true;

  /* If a `Node` is passed to sanitize(), then performs sanitization in-place instead
   * of importing it into a new Document and returning a sanitized copy */
  let IN_PLACE = false;

  /* Allow usage of profiles like html, svg and mathMl */
  let USE_PROFILES = {};

  /* Tags to ignore content of when KEEP_CONTENT is true */
  let FORBID_CONTENTS = null;
  const DEFAULT_FORBID_CONTENTS = addToSet({}, [
    'annotation-xml',
    'audio',
    'colgroup',
    'desc',
    'foreignobject',
    'head',
    'iframe',
    'math',
    'mi',
    'mn',
    'mo',
    'ms',
    'mtext',
    'noembed',
    'noframes',
    'noscript',
    'plaintext',
    'script',
    'style',
    'svg',
    'template',
    'thead',
    'title',
    'video',
    'xmp',
  ]);

  /* Tags that are safe for data: URIs */
  let DATA_URI_TAGS = null;
  const DEFAULT_DATA_URI_TAGS = addToSet({}, [
    'audio',
    'video',
    'img',
    'source',
    'image',
    'track',
  ]);

  /* Attributes safe for values like "javascript:" */
  let URI_SAFE_ATTRIBUTES = null;
  const DEFAULT_URI_SAFE_ATTRIBUTES = addToSet({}, [
    'alt',
    'class',
    'for',
    'id',
    'label',
    'name',
    'pattern',
    'placeholder',
    'role',
    'summary',
    'title',
    'value',
    'style',
    'xmlns',
  ]);

  const MATHML_NAMESPACE = 'http://www.w3.org/1998/Math/MathML';
  const SVG_NAMESPACE = 'http://www.w3.org/2000/svg';
  const HTML_NAMESPACE = 'http://www.w3.org/1999/xhtml';
  /* Document namespace */
  let NAMESPACE = HTML_NAMESPACE;
  let IS_EMPTY_INPUT = false;

  /* Parsing of strict XHTML documents */
  let PARSER_MEDIA_TYPE;
  const SUPPORTED_PARSER_MEDIA_TYPES = ['application/xhtml+xml', 'text/html'];
  const DEFAULT_PARSER_MEDIA_TYPE = 'text/html';
  let transformCaseFunc;

  /* Keep a reference to config to pass to hooks */
  let CONFIG = null;

  /* Ideally, do not touch anything below this line */
  /* ______________________________________________ */

  const formElement = document.createElement('form');

  const isRegexOrFunction = function (testValue) {
    return testValue instanceof RegExp || testValue instanceof Function;
  };

  /**
   * _parseConfig
   *
   * @param  {Object} cfg optional config literal
   */
  // eslint-disable-next-line complexity
  const _parseConfig = function (cfg) {
    if (CONFIG && CONFIG === cfg) {
      return;
    }

    /* Shield configuration object from tampering */
    if (!cfg || typeof cfg !== 'object') {
      cfg = {};
    }

    /* Shield configuration object from prototype pollution */
    cfg = clone(cfg);

    PARSER_MEDIA_TYPE =
      // eslint-disable-next-line unicorn/prefer-includes
      SUPPORTED_PARSER_MEDIA_TYPES.indexOf(cfg.PARSER_MEDIA_TYPE) === -1
        ? (PARSER_MEDIA_TYPE = DEFAULT_PARSER_MEDIA_TYPE)
        : (PARSER_MEDIA_TYPE = cfg.PARSER_MEDIA_TYPE);

    // HTML tags and attributes are not case-sensitive, converting to lowercase. Keeping XHTML as is.
    transformCaseFunc =
      PARSER_MEDIA_TYPE === 'application/xhtml+xml'
        ? (x) => x
        : stringToLowerCase;

    /* Set configuration parameters */
    ALLOWED_TAGS =
      'ALLOWED_TAGS' in cfg
        ? addToSet({}, cfg.ALLOWED_TAGS, transformCaseFunc)
        : DEFAULT_ALLOWED_TAGS;
    ALLOWED_ATTR =
      'ALLOWED_ATTR' in cfg
        ? addToSet({}, cfg.ALLOWED_ATTR, transformCaseFunc)
        : DEFAULT_ALLOWED_ATTR;
    URI_SAFE_ATTRIBUTES =
      'ADD_URI_SAFE_ATTR' in cfg
        ? addToSet(
            clone(DEFAULT_URI_SAFE_ATTRIBUTES),
            cfg.ADD_URI_SAFE_ATTR,
            transformCaseFunc
          )
        : DEFAULT_URI_SAFE_ATTRIBUTES;
    DATA_URI_TAGS =
      'ADD_DATA_URI_TAGS' in cfg
        ? addToSet(
            clone(DEFAULT_DATA_URI_TAGS),
            cfg.ADD_DATA_URI_TAGS,
            transformCaseFunc
          )
        : DEFAULT_DATA_URI_TAGS;
    FORBID_CONTENTS =
      'FORBID_CONTENTS' in cfg
        ? addToSet({}, cfg.FORBID_CONTENTS, transformCaseFunc)
        : DEFAULT_FORBID_CONTENTS;
    FORBID_TAGS =
      'FORBID_TAGS' in cfg
        ? addToSet({}, cfg.FORBID_TAGS, transformCaseFunc)
        : {};
    FORBID_ATTR =
      'FORBID_ATTR' in cfg
        ? addToSet({}, cfg.FORBID_ATTR, transformCaseFunc)
        : {};
    USE_PROFILES = 'USE_PROFILES' in cfg ? cfg.USE_PROFILES : false;
    ALLOW_ARIA_ATTR = cfg.ALLOW_ARIA_ATTR !== false; // Default true
    ALLOW_DATA_ATTR = cfg.ALLOW_DATA_ATTR !== false; // Default true
    ALLOW_UNKNOWN_PROTOCOLS = cfg.ALLOW_UNKNOWN_PROTOCOLS || false; // Default false
    SAFE_FOR_TEMPLATES = cfg.SAFE_FOR_TEMPLATES || false; // Default false
    WHOLE_DOCUMENT = cfg.WHOLE_DOCUMENT || false; // Default false
    RETURN_DOM = cfg.RETURN_DOM || false; // Default false
    RETURN_DOM_FRAGMENT = cfg.RETURN_DOM_FRAGMENT || false; // Default false
    RETURN_TRUSTED_TYPE = cfg.RETURN_TRUSTED_TYPE || false; // Default false
    FORCE_BODY = cfg.FORCE_BODY || false; // Default false
    SANITIZE_DOM = cfg.SANITIZE_DOM !== false; // Default true
    KEEP_CONTENT = cfg.KEEP_CONTENT !== false; // Default true
    IN_PLACE = cfg.IN_PLACE || false; // Default false
    IS_ALLOWED_URI = cfg.ALLOWED_URI_REGEXP || IS_ALLOWED_URI;
    NAMESPACE = cfg.NAMESPACE || HTML_NAMESPACE;
    if (
      cfg.CUSTOM_ELEMENT_HANDLING &&
      isRegexOrFunction(cfg.CUSTOM_ELEMENT_HANDLING.tagNameCheck)
    ) {
      CUSTOM_ELEMENT_HANDLING.tagNameCheck =
        cfg.CUSTOM_ELEMENT_HANDLING.tagNameCheck;
    }

    if (
      cfg.CUSTOM_ELEMENT_HANDLING &&
      isRegexOrFunction(cfg.CUSTOM_ELEMENT_HANDLING.attributeNameCheck)
    ) {
      CUSTOM_ELEMENT_HANDLING.attributeNameCheck =
        cfg.CUSTOM_ELEMENT_HANDLING.attributeNameCheck;
    }

    if (
      cfg.CUSTOM_ELEMENT_HANDLING &&
      typeof cfg.CUSTOM_ELEMENT_HANDLING.allowCustomizedBuiltInElements ===
        'boolean'
    ) {
      CUSTOM_ELEMENT_HANDLING.allowCustomizedBuiltInElements =
        cfg.CUSTOM_ELEMENT_HANDLING.allowCustomizedBuiltInElements;
    }

    if (SAFE_FOR_TEMPLATES) {
      ALLOW_DATA_ATTR = false;
    }

    if (RETURN_DOM_FRAGMENT) {
      RETURN_DOM = true;
    }

    /* Parse profile info */
    if (USE_PROFILES) {
      ALLOWED_TAGS = addToSet({}, [...TAGS.text]);
      ALLOWED_ATTR = [];
      if (USE_PROFILES.html === true) {
        addToSet(ALLOWED_TAGS, TAGS.html);
        addToSet(ALLOWED_ATTR, ATTRS.html);
      }

      if (USE_PROFILES.svg === true) {
        addToSet(ALLOWED_TAGS, TAGS.svg);
        addToSet(ALLOWED_ATTR, ATTRS.svg);
        addToSet(ALLOWED_ATTR, ATTRS.xml);
      }

      if (USE_PROFILES.svgFilters === true) {
        addToSet(ALLOWED_TAGS, TAGS.svgFilters);
        addToSet(ALLOWED_ATTR, ATTRS.svg);
        addToSet(ALLOWED_ATTR, ATTRS.xml);
      }

      if (USE_PROFILES.mathMl === true) {
        addToSet(ALLOWED_TAGS, TAGS.mathMl);
        addToSet(ALLOWED_ATTR, ATTRS.mathMl);
        addToSet(ALLOWED_ATTR, ATTRS.xml);
      }
    }

    /* Merge configuration parameters */
    if (cfg.ADD_TAGS) {
      if (ALLOWED_TAGS === DEFAULT_ALLOWED_TAGS) {
        ALLOWED_TAGS = clone(ALLOWED_TAGS);
      }

      addToSet(ALLOWED_TAGS, cfg.ADD_TAGS, transformCaseFunc);
    }

    if (cfg.ADD_ATTR) {
      if (ALLOWED_ATTR === DEFAULT_ALLOWED_ATTR) {
        ALLOWED_ATTR = clone(ALLOWED_ATTR);
      }

      addToSet(ALLOWED_ATTR, cfg.ADD_ATTR, transformCaseFunc);
    }

    if (cfg.ADD_URI_SAFE_ATTR) {
      addToSet(URI_SAFE_ATTRIBUTES, cfg.ADD_URI_SAFE_ATTR, transformCaseFunc);
    }

    if (cfg.FORBID_CONTENTS) {
      if (FORBID_CONTENTS === DEFAULT_FORBID_CONTENTS) {
        FORBID_CONTENTS = clone(FORBID_CONTENTS);
      }

      addToSet(FORBID_CONTENTS, cfg.FORBID_CONTENTS, transformCaseFunc);
    }

    /* Add #text in case KEEP_CONTENT is set to true */
    if (KEEP_CONTENT) {
      ALLOWED_TAGS['#text'] = true;
    }

    /* Add html, head and body to ALLOWED_TAGS in case WHOLE_DOCUMENT is true */
    if (WHOLE_DOCUMENT) {
      addToSet(ALLOWED_TAGS, ['html', 'head', 'body']);
    }

    /* Add tbody to ALLOWED_TAGS in case tables are permitted, see #286, #365 */
    if (ALLOWED_TAGS.table) {
      addToSet(ALLOWED_TAGS, ['tbody']);
      delete FORBID_TAGS.tbody;
    }

    // Prevent further manipulation of configuration.
    // Not available in IE8, Safari 5, etc.
    if (freeze) {
      freeze(cfg);
    }

    CONFIG = cfg;
  };

  const MATHML_TEXT_INTEGRATION_POINTS = addToSet({}, [
    'mi',
    'mo',
    'mn',
    'ms',
    'mtext',
  ]);

  const HTML_INTEGRATION_POINTS = addToSet({}, [
    'foreignobject',
    'desc',
    'title',
    'annotation-xml',
  ]);

  // Certain elements are allowed in both SVG and HTML
  // namespace. We need to specify them explicitly
  // so that they don't get erroneously deleted from
  // HTML namespace.
  const COMMON_SVG_AND_HTML_ELEMENTS = addToSet({}, [
    'title',
    'style',
    'font',
    'a',
    'script',
  ]);

  /* Keep track of all possible SVG and MathML tags
   * so that we can perform the namespace checks
   * correctly. */
  const ALL_SVG_TAGS = addToSet({}, TAGS.svg);
  addToSet(ALL_SVG_TAGS, TAGS.svgFilters);
  addToSet(ALL_SVG_TAGS, TAGS.svgDisallowed);

  const ALL_MATHML_TAGS = addToSet({}, TAGS.mathMl);
  addToSet(ALL_MATHML_TAGS, TAGS.mathMlDisallowed);

  /**
   *
   *
   * @param  {Element} element a DOM element whose namespace is being checked
   * @returns {boolean} Return false if the element has a
   *  namespace that a spec-compliant parser would never
   *  return. Return true otherwise.
   */
  const _checkValidNamespace = function (element) {
    let parent = getParentNode(element);

    // In JSDOM, if we're inside shadow DOM, then parentNode
    // can be null. We just simulate parent in this case.
    if (!parent || !parent.tagName) {
      parent = {
        namespaceURI: HTML_NAMESPACE,
        tagName: 'template',
      };
    }

    const tagName = stringToLowerCase(element.tagName);
    const parentTagName = stringToLowerCase(parent.tagName);

    if (element.namespaceURI === SVG_NAMESPACE) {
      // The only way to switch from HTML namespace to SVG
      // is via <svg>. If it happens via any other tag, then
      // it should be killed.
      if (parent.namespaceURI === HTML_NAMESPACE) {
        return tagName === 'svg';
      }

      // The only way to switch from MathML to SVG is via
      // svg if parent is either <annotation-xml> or MathML
      // text integration points.
      if (parent.namespaceURI === MATHML_NAMESPACE) {
        return (
          tagName === 'svg' &&
          (parentTagName === 'annotation-xml' ||
            MATHML_TEXT_INTEGRATION_POINTS[parentTagName])
        );
      }

      // We only allow elements that are defined in SVG
      // spec. All others are disallowed in SVG namespace.
      return Boolean(ALL_SVG_TAGS[tagName]);
    }

    if (element.namespaceURI === MATHML_NAMESPACE) {
      // The only way to switch from HTML namespace to MathML
      // is via <math>. If it happens via any other tag, then
      // it should be killed.
      if (parent.namespaceURI === HTML_NAMESPACE) {
        return tagName === 'math';
      }

      // The only way to switch from SVG to MathML is via
      // <math> and HTML integration points
      if (parent.namespaceURI === SVG_NAMESPACE) {
        return tagName === 'math' && HTML_INTEGRATION_POINTS[parentTagName];
      }

      // We only allow elements that are defined in MathML
      // spec. All others are disallowed in MathML namespace.
      return Boolean(ALL_MATHML_TAGS[tagName]);
    }

    if (element.namespaceURI === HTML_NAMESPACE) {
      // The only way to switch from SVG to HTML is via
      // HTML integration points, and from MathML to HTML
      // is via MathML text integration points
      if (
        parent.namespaceURI === SVG_NAMESPACE &&
        !HTML_INTEGRATION_POINTS[parentTagName]
      ) {
        return false;
      }

      if (
        parent.namespaceURI === MATHML_NAMESPACE &&
        !MATHML_TEXT_INTEGRATION_POINTS[parentTagName]
      ) {
        return false;
      }

      // We disallow tags that are specific for MathML
      // or SVG and should never appear in HTML namespace
      return (
        !ALL_MATHML_TAGS[tagName] &&
        (COMMON_SVG_AND_HTML_ELEMENTS[tagName] || !ALL_SVG_TAGS[tagName])
      );
    }

    // The code should never reach this place (this means
    // that the element somehow got namespace that is not
    // HTML, SVG or MathML). Return false just in case.
    return false;
  };

  /**
   * _forceRemove
   *
   * @param  {Node} node a DOM node
   */
  const _forceRemove = function (node) {
    arrayPush(DOMPurify.removed, { element: node });
    try {
      // eslint-disable-next-line unicorn/prefer-dom-node-remove
      node.parentNode.removeChild(node);
    } catch (_) {
      try {
        node.outerHTML = emptyHTML;
      } catch (_) {
        node.remove();
      }
    }
  };

  /**
   * _removeAttribute
   *
   * @param  {String} name an Attribute name
   * @param  {Node} node a DOM node
   */
  const _removeAttribute = function (name, node) {
    try {
      arrayPush(DOMPurify.removed, {
        attribute: node.getAttributeNode(name),
        from: node,
      });
    } catch (_) {
      arrayPush(DOMPurify.removed, {
        attribute: null,
        from: node,
      });
    }

    node.removeAttribute(name);

    // We void attribute values for unremovable "is"" attributes
    if (name === 'is' && !ALLOWED_ATTR[name]) {
      if (RETURN_DOM || RETURN_DOM_FRAGMENT) {
        try {
          _forceRemove(node);
        } catch (_) {}
      } else {
        try {
          node.setAttribute(name, '');
        } catch (_) {}
      }
    }
  };

  /**
   * _initDocument
   *
   * @param  {String} dirty a string of dirty markup
   * @return {Document} a DOM, filled with the dirty markup
   */
  const _initDocument = function (dirty) {
    /* Create a HTML document */
    let doc;
    let leadingWhitespace;

    if (FORCE_BODY) {
      dirty = '<remove></remove>' + dirty;
    } else {
      /* If FORCE_BODY isn't used, leading whitespace needs to be preserved manually */
      const matches = stringMatch(dirty, /^[\r\n\t ]+/);
      leadingWhitespace = matches && matches[0];
    }

    if (PARSER_MEDIA_TYPE === 'application/xhtml+xml') {
      // Root of XHTML doc must contain xmlns declaration (see https://www.w3.org/TR/xhtml1/normative.html#strict)
      dirty =
        '<html xmlns="http://www.w3.org/1999/xhtml"><head></head><body>' +
        dirty +
        '</body></html>';
    }

    const dirtyPayload = trustedTypesPolicy
      ? trustedTypesPolicy.createHTML(dirty)
      : dirty;
    /*
     * Use the DOMParser API by default, fallback later if needs be
     * DOMParser not work for svg when has multiple root element.
     */
    if (NAMESPACE === HTML_NAMESPACE) {
      try {
        doc = new DOMParser().parseFromString(dirtyPayload, PARSER_MEDIA_TYPE);
      } catch (_) {}
    }

    /* Use createHTMLDocument in case DOMParser is not available */
    if (!doc || !doc.documentElement) {
      doc = implementation.createDocument(NAMESPACE, 'template', null);
      try {
        doc.documentElement.innerHTML = IS_EMPTY_INPUT ? '' : dirtyPayload;
      } catch (_) {
        // Syntax error if dirtyPayload is invalid xml
      }
    }

    const body = doc.body || doc.documentElement;

    if (dirty && leadingWhitespace) {
      body.insertBefore(
        document.createTextNode(leadingWhitespace),
        body.childNodes[0] || null
      );
    }

    /* Work on whole document or just its body */
    if (NAMESPACE === HTML_NAMESPACE) {
      return getElementsByTagName.call(
        doc,
        WHOLE_DOCUMENT ? 'html' : 'body'
      )[0];
    }

    return WHOLE_DOCUMENT ? doc.documentElement : body;
  };

  /**
   * _createIterator
   *
   * @param  {Document} root document/fragment to create iterator for
   * @return {Iterator} iterator instance
   */
  const _createIterator = function (root) {
    return createNodeIterator.call(
      root.ownerDocument || root,
      root,
      // eslint-disable-next-line no-bitwise
      NodeFilter.SHOW_ELEMENT | NodeFilter.SHOW_COMMENT | NodeFilter.SHOW_TEXT,
      null,
      false
    );
  };

  /**
   * _isClobbered
   *
   * @param  {Node} elm element to check for clobbering attacks
   * @return {Boolean} true if clobbered, false if safe
   */
  const _isClobbered = function (elm) {
    return (
      elm instanceof HTMLFormElement &&
      (typeof elm.nodeName !== 'string' ||
        typeof elm.textContent !== 'string' ||
        typeof elm.removeChild !== 'function' ||
        !(elm.attributes instanceof NamedNodeMap) ||
        typeof elm.removeAttribute !== 'function' ||
        typeof elm.setAttribute !== 'function' ||
        typeof elm.namespaceURI !== 'string' ||
        typeof elm.insertBefore !== 'function')
    );
  };

  /**
   * _isNode
   *
   * @param  {Node} obj object to check whether it's a DOM node
   * @return {Boolean} true is object is a DOM node
   */
  const _isNode = function (object) {
    return typeof Node === 'object'
      ? object instanceof Node
      : object &&
          typeof object === 'object' &&
          typeof object.nodeType === 'number' &&
          typeof object.nodeName === 'string';
  };

  /**
   * _executeHook
   * Execute user configurable hooks
   *
   * @param  {String} entryPoint  Name of the hook's entry point
   * @param  {Node} currentNode node to work on with the hook
   * @param  {Object} data additional hook parameters
   */
  const _executeHook = function (entryPoint, currentNode, data) {
    if (!hooks[entryPoint]) {
      return;
    }

    arrayForEach(hooks[entryPoint], (hook) => {
      hook.call(DOMPurify, currentNode, data, CONFIG);
    });
  };

  /**
   * _sanitizeElements
   *
   * @protect nodeName
   * @protect textContent
   * @protect removeChild
   *
   * @param   {Node} currentNode to check for permission to exist
   * @return  {Boolean} true if node was killed, false if left alive
   */
  const _sanitizeElements = function (currentNode) {
    let content;

    /* Execute a hook if present */
    _executeHook('beforeSanitizeElements', currentNode, null);

    /* Check if element is clobbered or can clobber */
    if (_isClobbered(currentNode)) {
      _forceRemove(currentNode);
      return true;
    }

    /* Check if tagname contains Unicode */
    if (regExpTest(/[\u0080-\uFFFF]/, currentNode.nodeName)) {
      _forceRemove(currentNode);
      return true;
    }

    /* Now let's check the element's type and name */
    const tagName = transformCaseFunc(currentNode.nodeName);

    /* Execute a hook if present */
    _executeHook('uponSanitizeElement', currentNode, {
      tagName,
      allowedTags: ALLOWED_TAGS,
    });

    /* Detect mXSS attempts abusing namespace confusion */
    if (
      currentNode.hasChildNodes() &&
      !_isNode(currentNode.firstElementChild) &&
      (!_isNode(currentNode.content) ||
        !_isNode(currentNode.content.firstElementChild)) &&
      regExpTest(/<[/\w]/g, currentNode.innerHTML) &&
      regExpTest(/<[/\w]/g, currentNode.textContent)
    ) {
      _forceRemove(currentNode);
      return true;
    }

    /* Mitigate a problem with templates inside select */
    if (
      tagName === 'select' &&
      regExpTest(/<template/i, currentNode.innerHTML)
    ) {
      _forceRemove(currentNode);
      return true;
    }

    /* Remove element if anything forbids its presence */
    if (!ALLOWED_TAGS[tagName] || FORBID_TAGS[tagName]) {
      /* Check if we have a custom element to handle */
      if (!FORBID_TAGS[tagName] && _basicCustomElementTest(tagName)) {
        if (
          CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof RegExp &&
          regExpTest(CUSTOM_ELEMENT_HANDLING.tagNameCheck, tagName)
        )
          return false;
        if (
          CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof Function &&
          CUSTOM_ELEMENT_HANDLING.tagNameCheck(tagName)
        )
          return false;
      }

      /* Keep content except for bad-listed elements */
      if (KEEP_CONTENT && !FORBID_CONTENTS[tagName]) {
        const parentNode = getParentNode(currentNode) || currentNode.parentNode;
        const childNodes = getChildNodes(currentNode) || currentNode.childNodes;

        if (childNodes && parentNode) {
          const childCount = childNodes.length;

          for (let i = childCount - 1; i >= 0; --i) {
            parentNode.insertBefore(
              cloneNode(childNodes[i], true),
              getNextSibling(currentNode)
            );
          }
        }
      }

      _forceRemove(currentNode);
      return true;
    }

    /* Check whether element has a valid namespace */
    if (currentNode instanceof Element && !_checkValidNamespace(currentNode)) {
      _forceRemove(currentNode);
      return true;
    }

    if (
      (tagName === 'noscript' || tagName === 'noembed') &&
      regExpTest(/<\/no(script|embed)/i, currentNode.innerHTML)
    ) {
      _forceRemove(currentNode);
      return true;
    }

    /* Sanitize element content to be template-safe */
    if (SAFE_FOR_TEMPLATES && currentNode.nodeType === 3) {
      /* Get the element's text content */
      content = currentNode.textContent;
      content = stringReplace(content, MUSTACHE_EXPR, ' ');
      content = stringReplace(content, ERB_EXPR, ' ');
      if (currentNode.textContent !== content) {
        arrayPush(DOMPurify.removed, { element: currentNode.cloneNode() });
        currentNode.textContent = content;
      }
    }

    /* Execute a hook if present */
    _executeHook('afterSanitizeElements', currentNode, null);

    return false;
  };

  /**
   * _isValidAttribute
   *
   * @param  {string} lcTag Lowercase tag name of containing element.
   * @param  {string} lcName Lowercase attribute name.
   * @param  {string} value Attribute value.
   * @return {Boolean} Returns true if `value` is valid, otherwise false.
   */
  // eslint-disable-next-line complexity
  const _isValidAttribute = function (lcTag, lcName, value) {
    /* Make sure attribute cannot clobber */
    if (
      SANITIZE_DOM &&
      (lcName === 'id' || lcName === 'name') &&
      (value in document || value in formElement)
    ) {
      return false;
    }

    /* Allow valid data-* attributes: At least one character after "-"
        (https://html.spec.whatwg.org/multipage/dom.html#embedding-custom-non-visible-data-with-the-data-*-attributes)
        XML-compatible (https://html.spec.whatwg.org/multipage/infrastructure.html#xml-compatible and http://www.w3.org/TR/xml/#d0e804)
        We don't need to check the value; it's always URI safe. */
    if (
      ALLOW_DATA_ATTR &&
      !FORBID_ATTR[lcName] &&
      regExpTest(DATA_ATTR, lcName)
    ) {
      // This attribute is safe
    } else if (ALLOW_ARIA_ATTR && regExpTest(ARIA_ATTR, lcName)) {
      // This attribute is safe
      /* Otherwise, check the name is permitted */
    } else if (!ALLOWED_ATTR[lcName] || FORBID_ATTR[lcName]) {
      if (
        // First condition does a very basic check if a) it's basically a valid custom element tagname AND
        // b) if the tagName passes whatever the user has configured for CUSTOM_ELEMENT_HANDLING.tagNameCheck
        // and c) if the attribute name passes whatever the user has configured for CUSTOM_ELEMENT_HANDLING.attributeNameCheck
        (_basicCustomElementTest(lcTag) &&
          ((CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof RegExp &&
            regExpTest(CUSTOM_ELEMENT_HANDLING.tagNameCheck, lcTag)) ||
            (CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof Function &&
              CUSTOM_ELEMENT_HANDLING.tagNameCheck(lcTag))) &&
          ((CUSTOM_ELEMENT_HANDLING.attributeNameCheck instanceof RegExp &&
            regExpTest(CUSTOM_ELEMENT_HANDLING.attributeNameCheck, lcName)) ||
            (CUSTOM_ELEMENT_HANDLING.attributeNameCheck instanceof Function &&
              CUSTOM_ELEMENT_HANDLING.attributeNameCheck(lcName)))) ||
        // Alternative, second condition checks if it's an `is`-attribute, AND
        // the value passes whatever the user has configured for CUSTOM_ELEMENT_HANDLING.tagNameCheck
        (lcName === 'is' &&
          CUSTOM_ELEMENT_HANDLING.allowCustomizedBuiltInElements &&
          ((CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof RegExp &&
            regExpTest(CUSTOM_ELEMENT_HANDLING.tagNameCheck, value)) ||
            (CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof Function &&
              CUSTOM_ELEMENT_HANDLING.tagNameCheck(value))))
      ) {
        // If user has supplied a regexp or function in CUSTOM_ELEMENT_HANDLING.tagNameCheck, we need to also allow derived custom elements using the same tagName test.
        // Additionally, we need to allow attributes passing the CUSTOM_ELEMENT_HANDLING.attributeNameCheck user has configured, as custom elements can define these at their own discretion.
      } else {
        return false;
      }
      /* Check value is safe. First, is attr inert? If so, is safe */
    } else if (URI_SAFE_ATTRIBUTES[lcName]) {
      // This attribute is safe
      /* Check no script, data or unknown possibly unsafe URI
        unless we know URI values are safe for that attribute */
    } else if (
      regExpTest(IS_ALLOWED_URI, stringReplace(value, ATTR_WHITESPACE, ''))
    ) {
      // This attribute is safe
      /* Keep image data URIs alive if src/xlink:href is allowed */
      /* Further prevent gadget XSS for dynamically built script tags */
    } else if (
      (lcName === 'src' || lcName === 'xlink:href' || lcName === 'href') &&
      lcTag !== 'script' &&
      stringIndexOf(value, 'data:') === 0 &&
      DATA_URI_TAGS[lcTag]
    ) {
      // This attribute is safe
      /* Allow unknown protocols: This provides support for links that
        are handled by protocol handlers which may be unknown ahead of
        time, e.g. fb:, spotify: */
    } else if (
      ALLOW_UNKNOWN_PROTOCOLS &&
      !regExpTest(IS_SCRIPT_OR_DATA, stringReplace(value, ATTR_WHITESPACE, ''))
    ) {
      // This attribute is safe
      /* Check for binary attributes */
      // eslint-disable-next-line no-negated-condition
    } else if (!value) {
      // Binary attributes are safe at this point
      /* Anything else, presume unsafe, do not add it back */
    } else {
      return false;
    }

    return true;
  };

  /**
   * _basicCustomElementCheck
   * checks if at least one dash is included in tagName, and it's not the first char
   * for more sophisticated checking see https://github.com/sindresorhus/validate-element-name
   * @param {string} tagName name of the tag of the node to sanitize
   */
  const _basicCustomElementTest = function (tagName) {
    return tagName.indexOf('-') > 0;
  };

  /**
   * _sanitizeAttributes
   *
   * @protect attributes
   * @protect nodeName
   * @protect removeAttribute
   * @protect setAttribute
   *
   * @param  {Node} currentNode to sanitize
   */
  const _sanitizeAttributes = function (currentNode) {
    let attr;
    let value;
    let lcName;
    let l;
    /* Execute a hook if present */
    _executeHook('beforeSanitizeAttributes', currentNode, null);

    const { attributes } = currentNode;

    /* Check if we have attributes; if not we might have a text node */
    if (!attributes) {
      return;
    }

    const hookEvent = {
      attrName: '',
      attrValue: '',
      keepAttr: true,
      allowedAttributes: ALLOWED_ATTR,
    };
    l = attributes.length;

    /* Go backwards over all attributes; safely remove bad ones */
    while (l--) {
      attr = attributes[l];
      const { name, namespaceURI } = attr;
      value = name === 'value' ? attr.value : stringTrim(attr.value);
      lcName = transformCaseFunc(name);

      /* Execute a hook if present */
      hookEvent.attrName = lcName;
      hookEvent.attrValue = value;
      hookEvent.keepAttr = true;
      hookEvent.forceKeepAttr = undefined; // Allows developers to see this is a property they can set
      _executeHook('uponSanitizeAttribute', currentNode, hookEvent);
      value = hookEvent.attrValue;
      /* Did the hooks approve of the attribute? */
      if (hookEvent.forceKeepAttr) {
        continue;
      }

      /* Remove attribute */
      _removeAttribute(name, currentNode);

      /* Did the hooks approve of the attribute? */
      if (!hookEvent.keepAttr) {
        continue;
      }

      /* Work around a security issue in jQuery 3.0 */
      if (regExpTest(/\/>/i, value)) {
        _removeAttribute(name, currentNode);
        continue;
      }

      /* Sanitize attribute content to be template-safe */
      if (SAFE_FOR_TEMPLATES) {
        value = stringReplace(value, MUSTACHE_EXPR, ' ');
        value = stringReplace(value, ERB_EXPR, ' ');
      }

      /* Is `value` valid for this attribute? */
      const lcTag = transformCaseFunc(currentNode.nodeName);
      if (!_isValidAttribute(lcTag, lcName, value)) {
        continue;
      }

      /* Handle invalid data-* attribute set by try-catching it */
      try {
        if (namespaceURI) {
          currentNode.setAttributeNS(namespaceURI, name, value);
        } else {
          /* Fallback to setAttribute() for browser-unrecognized namespaces e.g. "x-schema". */
          currentNode.setAttribute(name, value);
        }

        arrayPop(DOMPurify.removed);
      } catch (_) {}
    }

    /* Execute a hook if present */
    _executeHook('afterSanitizeAttributes', currentNode, null);
  };

  /**
   * _sanitizeShadowDOM
   *
   * @param  {DocumentFragment} fragment to iterate over recursively
   */
  const _sanitizeShadowDOM = function (fragment) {
    let shadowNode;
    const shadowIterator = _createIterator(fragment);

    /* Execute a hook if present */
    _executeHook('beforeSanitizeShadowDOM', fragment, null);

    while ((shadowNode = shadowIterator.nextNode())) {
      /* Execute a hook if present */
      _executeHook('uponSanitizeShadowNode', shadowNode, null);

      /* Sanitize tags and elements */
      if (_sanitizeElements(shadowNode)) {
        continue;
      }

      /* Deep shadow DOM detected */
      if (shadowNode.content instanceof DocumentFragment) {
        _sanitizeShadowDOM(shadowNode.content);
      }

      /* Check attributes, sanitize if necessary */
      _sanitizeAttributes(shadowNode);
    }

    /* Execute a hook if present */
    _executeHook('afterSanitizeShadowDOM', fragment, null);
  };

  /**
   * Sanitize
   * Public method providing core sanitation functionality
   *
   * @param {String|Node} dirty string or DOM node
   * @param {Object} configuration object
   */
  // eslint-disable-next-line complexity
  DOMPurify.sanitize = function (dirty, cfg) {
    let body;
    let importedNode;
    let currentNode;
    let oldNode;
    let returnNode;
    /* Make sure we have a string to sanitize.
      DO NOT return early, as this will return the wrong type if
      the user has requested a DOM object rather than a string */
    IS_EMPTY_INPUT = !dirty;
    if (IS_EMPTY_INPUT) {
      dirty = '<!-->';
    }

    /* Stringify, in case dirty is an object */
    if (typeof dirty !== 'string' && !_isNode(dirty)) {
      // eslint-disable-next-line no-negated-condition
      if (typeof dirty.toString !== 'function') {
        throw typeErrorCreate('toString is not a function');
      } else {
        dirty = dirty.toString();
        if (typeof dirty !== 'string') {
          throw typeErrorCreate('dirty is not a string, aborting');
        }
      }
    }

    /* Check we can run. Otherwise fall back or ignore */
    if (!DOMPurify.isSupported) {
      if (
        typeof window.toStaticHTML === 'object' ||
        typeof window.toStaticHTML === 'function'
      ) {
        if (typeof dirty === 'string') {
          return window.toStaticHTML(dirty);
        }

        if (_isNode(dirty)) {
          return window.toStaticHTML(dirty.outerHTML);
        }
      }

      return dirty;
    }

    /* Assign config vars */
    if (!SET_CONFIG) {
      _parseConfig(cfg);
    }

    /* Clean up removed elements */
    DOMPurify.removed = [];

    /* Check if dirty is correctly typed for IN_PLACE */
    if (typeof dirty === 'string') {
      IN_PLACE = false;
    }

    if (IN_PLACE) {
      /* Do some early pre-sanitization to avoid unsafe root nodes */
      if (dirty.nodeName) {
        const tagName = transformCaseFunc(dirty.nodeName);
        if (!ALLOWED_TAGS[tagName] || FORBID_TAGS[tagName]) {
          throw typeErrorCreate(
            'root node is forbidden and cannot be sanitized in-place'
          );
        }
      }
    } else if (dirty instanceof Node) {
      /* If dirty is a DOM element, append to an empty document to avoid
         elements being stripped by the parser */
      body = _initDocument('<!---->');
      importedNode = body.ownerDocument.importNode(dirty, true);
      if (importedNode.nodeType === 1 && importedNode.nodeName === 'BODY') {
        /* Node is already a body, use as is */
        body = importedNode;
      } else if (importedNode.nodeName === 'HTML') {
        body = importedNode;
      } else {
        // eslint-disable-next-line unicorn/prefer-dom-node-append
        body.appendChild(importedNode);
      }
    } else {
      /* Exit directly if we have nothing to do */
      if (
        !RETURN_DOM &&
        !SAFE_FOR_TEMPLATES &&
        !WHOLE_DOCUMENT &&
        // eslint-disable-next-line unicorn/prefer-includes
        dirty.indexOf('<') === -1
      ) {
        return trustedTypesPolicy && RETURN_TRUSTED_TYPE
          ? trustedTypesPolicy.createHTML(dirty)
          : dirty;
      }

      /* Initialize the document to work on */
      body = _initDocument(dirty);

      /* Check we have a DOM node from the data */
      if (!body) {
        return RETURN_DOM ? null : RETURN_TRUSTED_TYPE ? emptyHTML : '';
      }
    }

    /* Remove first element node (ours) if FORCE_BODY is set */
    if (body && FORCE_BODY) {
      _forceRemove(body.firstChild);
    }

    /* Get node iterator */
    const nodeIterator = _createIterator(IN_PLACE ? dirty : body);

    /* Now start iterating over the created document */
    while ((currentNode = nodeIterator.nextNode())) {
      /* Fix IE's strange behavior with manipulated textNodes #89 */
      if (currentNode.nodeType === 3 && currentNode === oldNode) {
        continue;
      }

      /* Sanitize tags and elements */
      if (_sanitizeElements(currentNode)) {
        continue;
      }

      /* Shadow DOM detected, sanitize it */
      if (currentNode.content instanceof DocumentFragment) {
        _sanitizeShadowDOM(currentNode.content);
      }

      /* Check attributes, sanitize if necessary */
      _sanitizeAttributes(currentNode);

      oldNode = currentNode;
    }

    oldNode = null;

    /* If we sanitized `dirty` in-place, return it. */
    if (IN_PLACE) {
      return dirty;
    }

    /* Return sanitized string or DOM */
    if (RETURN_DOM) {
      if (RETURN_DOM_FRAGMENT) {
        returnNode = createDocumentFragment.call(body.ownerDocument);

        while (body.firstChild) {
          // eslint-disable-next-line unicorn/prefer-dom-node-append
          returnNode.appendChild(body.firstChild);
        }
      } else {
        returnNode = body;
      }

      if (ALLOWED_ATTR.shadowroot) {
        /*
          AdoptNode() is not used because internal state is not reset
          (e.g. the past names map of a HTMLFormElement), this is safe
          in theory but we would rather not risk another attack vector.
          The state that is cloned by importNode() is explicitly defined
          by the specs.
        */
        returnNode = importNode.call(originalDocument, returnNode, true);
      }

      return returnNode;
    }

    let serializedHTML = WHOLE_DOCUMENT ? body.outerHTML : body.innerHTML;

    /* Serialize doctype if allowed */
    if (
      WHOLE_DOCUMENT &&
      ALLOWED_TAGS['!doctype'] &&
      body.ownerDocument &&
      body.ownerDocument.doctype &&
      body.ownerDocument.doctype.name &&
      regExpTest(EXPRESSIONS.DOCTYPE_NAME, body.ownerDocument.doctype.name)
    ) {
      serializedHTML =
        '<!DOCTYPE ' + body.ownerDocument.doctype.name + '>\n' + serializedHTML;
    }

    /* Sanitize final string template-safe */
    if (SAFE_FOR_TEMPLATES) {
      serializedHTML = stringReplace(serializedHTML, MUSTACHE_EXPR, ' ');
      serializedHTML = stringReplace(serializedHTML, ERB_EXPR, ' ');
    }

    return trustedTypesPolicy && RETURN_TRUSTED_TYPE
      ? trustedTypesPolicy.createHTML(serializedHTML)
      : serializedHTML;
  };

  /**
   * Public method to set the configuration once
   * setConfig
   *
   * @param {Object} cfg configuration object
   */
  DOMPurify.setConfig = function (cfg) {
    _parseConfig(cfg);
    SET_CONFIG = true;
  };

  /**
   * Public method to remove the configuration
   * clearConfig
   *
   */
  DOMPurify.clearConfig = function () {
    CONFIG = null;
    SET_CONFIG = false;
  };

  /**
   * Public method to check if an attribute value is valid.
   * Uses last set config, if any. Otherwise, uses config defaults.
   * isValidAttribute
   *
   * @param  {string} tag Tag name of containing element.
   * @param  {string} attr Attribute name.
   * @param  {string} value Attribute value.
   * @return {Boolean} Returns true if `value` is valid. Otherwise, returns false.
   */
  DOMPurify.isValidAttribute = function (tag, attr, value) {
    /* Initialize shared config vars if necessary. */
    if (!CONFIG) {
      _parseConfig({});
    }

    const lcTag = transformCaseFunc(tag);
    const lcName = transformCaseFunc(attr);
    return _isValidAttribute(lcTag, lcName, value);
  };

  /**
   * AddHook
   * Public method to add DOMPurify hooks
   *
   * @param {String} entryPoint entry point for the hook to add
   * @param {Function} hookFunction function to execute
   */
  DOMPurify.addHook = function (entryPoint, hookFunction) {
    if (typeof hookFunction !== 'function') {
      return;
    }

    hooks[entryPoint] = hooks[entryPoint] || [];
    arrayPush(hooks[entryPoint], hookFunction);
  };

  /**
   * RemoveHook
   * Public method to remove a DOMPurify hook at a given entryPoint
   * (pops it from the stack of hooks if more are present)
   *
   * @param {String} entryPoint entry point for the hook to remove
   * @return {Function} removed(popped) hook
   */
  DOMPurify.removeHook = function (entryPoint) {
    if (hooks[entryPoint]) {
      return arrayPop(hooks[entryPoint]);
    }
  };

  /**
   * RemoveHooks
   * Public method to remove all DOMPurify hooks at a given entryPoint
   *
   * @param  {String} entryPoint entry point for the hooks to remove
   */
  DOMPurify.removeHooks = function (entryPoint) {
    if (hooks[entryPoint]) {
      hooks[entryPoint] = [];
    }
  };

  /**
   * RemoveAllHooks
   * Public method to remove all DOMPurify hooks
   *
   */
  DOMPurify.removeAllHooks = function () {
    hooks = {};
  };

  return DOMPurify;
}

export default createDOMPurify();