workbox-precaching/PrecacheFallbackPlugin.js

/*
  Copyright 2020 Google LLC

  Use of this source code is governed by an MIT-style
  license that can be found in the LICENSE file or at
  https://opensource.org/licenses/MIT.
*/
import { getOrCreatePrecacheController } from './utils/getOrCreatePrecacheController.js';
import './_version.js';
/**
 * `PrecacheFallbackPlugin` allows you to specify an "offline fallback"
 * response to be used when a given strategy is unable to generate a response.
 *
 * It does this by intercepting the `handlerDidError` plugin callback
 * and returning a precached response, taking the expected revision parameter
 * into account automatically.
 *
 * Unless you explicitly pass in a `PrecacheController` instance to the
 * constructor, the default instance will be used. Generally speaking, most
 * developers will end up using the default.
 *
 * @memberof workbox-precaching
 */
class PrecacheFallbackPlugin {
    /**
     * Constructs a new PrecacheFallbackPlugin with the associated fallbackURL.
     *
     * @param {Object} config
     * @param {string} config.fallbackURL A precached URL to use as the fallback
     *     if the associated strategy can't generate a response.
     * @param {PrecacheController} [config.precacheController] An optional
     *     PrecacheController instance. If not provided, the default
     *     PrecacheController will be used.
     */
    constructor({ fallbackURL, precacheController, }) {
        /**
         * @return {Promise<Response>} The precache response for the fallback URL.
         *
         * @private
         */
        this.handlerDidError = () => this._precacheController.matchPrecache(this._fallbackURL);
        this._fallbackURL = fallbackURL;
        this._precacheController =
            precacheController || getOrCreatePrecacheController();
    }
}
export { PrecacheFallbackPlugin };