/**
@license
Copyright (c) 2018 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
The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
Code distributed by Google as part of the polymer project is also
subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
*/
/**
  Utility method that updates the page's open graph and Twitter card metadata.
  It takes an object as a parameter with the following properties:
  title | description | url | image.

  If the `url` is not specified, `window.location.href` will be used; for
  all other properties, if they aren't specified, then that metadata field will not
  be set.

  Example (in your top level element or document, or in the router callback):

      import { updateMetadata } from 'pwa-helpers/metadata.js';

      updateMetadata({
        title: 'My App - view 1',
        description: 'This is my sample app',
        url: window.location.href,
        image: '/assets/view1-hero.png'
      });

*/
export declare const updateMetadata: ({ title, description, url, image, imageAlt }: {
    title?: string | undefined;
    description?: string | undefined;
    url?: string | undefined;
    image?: string | undefined;
    imageAlt?: string | undefined;
}) => void;
/**
  Utility method to create or update the content of a meta tag based on an
  attribute name/value pair.

  Example (in your top level element or document, or in the router callback):

      import { setMetaTag } from 'pwa-helpers/metadata.js';

      setMetaTag('name', 'twitter:card', 'summary');
      
  This would create the following meta tag in the head of the document (or
  update the content attribute if a meta tag with name="twitter:card" exists):

      <meta name="twitter:card" content="summary">

*/
export declare function setMetaTag(attrName: string, attrValue: string, content: string): void;