scroll-timeline-polyfill/src/index.js

A polyfill for scroll-driven animations on the web via ScrollTimeline

// Copyright 2019 Google LLC
//
// 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
//
//     https://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.

import {
  ScrollTimeline,
  ViewTimeline,
} from "./scroll-timeline-base";
import {
  animate,
  elementGetAnimations,
  documentGetAnimations,
  ProxyAnimation
} from "./proxy-animation.js";

import { initCSSPolyfill } from "./scroll-timeline-css"

function initPolyfill() {
  // initCSSPolyfill returns true iff the host browser supports SDA
  if (initCSSPolyfill()) {
    return;
  }

  if (
    !Reflect.defineProperty(window, 'ScrollTimeline', { value: ScrollTimeline })
  ) {
    throw Error(
      'Error installing ScrollTimeline polyfill: could not attach ScrollTimeline to window'
    );
  }
  if (
    !Reflect.defineProperty(window, 'ViewTimeline', { value: ViewTimeline })
  ) {
    throw Error(
      'Error installing ViewTimeline polyfill: could not attach ViewTimeline to window'
    );
  }

  if (
    !Reflect.defineProperty(Element.prototype, 'animate', { value: animate })
  ) {
    throw Error(
      "Error installing ScrollTimeline polyfill: could not attach WAAPI's animate to DOM Element"
    );
  }
  if (!Reflect.defineProperty(window, 'Animation', { value: ProxyAnimation })) {
    throw Error('Error installing Animation constructor.');
  }
  if (!Reflect.defineProperty(Element.prototype, "getAnimations", { value: elementGetAnimations })) {
    throw Error(
      "Error installing ScrollTimeline polyfill: could not attach WAAPI's getAnimations to DOM Element"
    );
  }
  if (!Reflect.defineProperty(document, "getAnimations", { value: documentGetAnimations })) {
    throw Error(
      "Error installing ScrollTimeline polyfill: could not attach WAAPI's getAnimations to document"
    );
  }
}

initPolyfill();