common-signals.js

/**
 * Copyright 2017 The AMP HTML Authors. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS-IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * Commonly used signals across different elements and documents.
 * @enum {string}
 */
export const CommonSignals = {
  /**
   * The element has been upgraded from ElementStub to its real implementation.
   */
  UPGRADED: 'upgraded',

  /**
   * The element has been built.
   */
  BUILT: 'built',

  /**
   * The element has started loading.
   * LOAD_START triggers at the start of the layoutCallback.
   */
  LOAD_START: 'load-start',

  /**
   * Rendering has been confirmed to have been started.
   * It is a signal to indicate meaningful display (e.g. text could be displayed
   * CSS is correctly installed/applied).
   *
   * Elements can optionally implement RENDER_START signal. (e.g. ad, shadowdoc)
   * if it want to define its own meaningful display time and toggle visibility.
   *
   * Simpler elements's RENDER_START can be equal to the start of the
   * buildCallback
   */
  RENDER_START: 'render-start',

  /**
   * The element has been loaded.
   * LOAD_END triggers at the end of the layoutCallback.
   *
   */
  LOAD_END: 'load-end',

  /**
   * The initial contents of an element/document/embed have been loaded.
   * INI_LOAD is an optional signal, implemented by ads, story, and elements
   * that consist of other resources.
   * It instructs that all critical resources has been loaded, and can be used
   * for more accurate visibility measurement.
   * When an element doesn't consist multiple child resources, LOAD_END signal
   * can be used to indicate resource load completion.
   * Note: Based on the implementation, INI_LOAD can trigger before or after
   * LOAD_END.
   */
  INI_LOAD: 'ini-load',

  /**
   * The element has been unlaid out.
   */
  UNLOAD: 'unload',
};