Class Meta

packages/platform-browser/src/browser/meta.ts:59–173

 */
@Service()
export class Meta {
  private readonly _doc = inject(DOCUMENT);
  private readonly _dom = getDOM();
  private _cachedHead: HTMLHeadElement | undefined;

  /**
   * Retrieves or creates a specific `<meta>` tag element in the current HTML document.
   * In searching for an existing tag, Angular attempts to match the `name` or `property` attribute
   * values in the provided tag definition, and verifies that all other attribute values are equal.
   * If an existing element is found, it is returned and is not modified in any way.
   * @param tag The definition of a `<meta>` element to match or create.
   * @param forceCreation True to create a new element without checking whether one already exists.
   * @returns The existing element with the same attributes and values if found,
   * the new element if no match is found, or `null` if the tag parameter is not defined.
   */
  addTag(tag: MetaDefinition, forceCreation: boolean = false): HTMLMetaElement | null {
    if (!tag) return null;
    return this._getOrCreateElement(tag, forceCreation);
  }

  /**
   * Retrieves or creates a set of `<meta>` tag elements in the current HTML document.
   * In searching for an existing tag, Angular attempts to match the `name` or `property` attribute
   * values in the provided tag definition, and verifies that all other attribute values are equal.
   * @param tags An array of tag definitions to match or create.
   * @param forceCreation True to create new elements without checking whether they already exist.
   * @returns The matching elements if found, or the new elements.
   */
  addTags(tags: MetaDefinition[], forceCreation: boolean = false): HTMLMetaElement[] {
    return tags
      .filter((tag): tag is MetaDefinition => !!tag)
      .map((tag) => this._getOrCreateElement(tag, forceCreation));
  }

  /**
   * Retrieves a `<meta>` tag element in the current HTML document.
   * @param attrSelector The tag attribute and value to match against, in the format
   * `"tag_attribute='value string'"`.
   * @returns The matching element, if any.
   */
  getTag(attrSelector: string): HTMLMetaElement | null {
    if (!attrSelector) return null;
    const meta = this._doc.querySelector<HTMLMetaElement>(buildMetaSelector(attrSelector));
    return isMetaTag(meta) ? meta : null;
  }

  /**
   * Retrieves a set of `<meta>` tag elements in the current HTML document.
   * @param attrSelector The tag attribute and value to match against, in the format
   * `"tag_attribute='value string'"`.
   * @returns The matching elements, if any.
   */
  getTags(attrSelector: string): HTMLMetaElement[] {
    if (!attrSelector) return [];
    const list = this._doc.querySelectorAll<HTMLMetaElement>(buildMetaSelector(attrSelector));
    return list ? Array.from(list).filter((elem) => isMetaTag(elem)) : [];
  }