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/**
* @license
* Copyright (C) 2016 The Android Open Source Project
*
* 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.
*/
export interface LibraryConfig {
/** Path to the library to be loaded. */
src: string;
/**
* Optional check to see if the library has already been loaded outside of
* this class. If this returns true, src will not be loaded, but
* configureCallback will be run if present.
*/
checkPresent?: () => boolean;
/**
* Optional library initialization to be run once after loading the library,
* before resolving promises for getLibrary(). Promises returned from
* getLibrary() will resolve to the return value of this function, if any.
*/
configureCallback?: () => unknown;
}
export class GrLibLoader {
/*
* Pending library loads, keyed by library config, populated when getLibrary()
* is first called for a given config. This retains the promise for each
* library so that later calls of getLibrary() for the same config can
* directly return a resolved promise.
*/
private readonly libraries = new Map<LibraryConfig, Promise<unknown>>();
_getPath(src: string) {
const root = this._getLibRoot();
return root ? root + src : null;
}
getLibrary(config: LibraryConfig): Promise<unknown> {
if (!this.libraries.has(config)) {
const loaded =
config.checkPresent && config.checkPresent()
? Promise.resolve()
: this._loadScript(this._getPath(config.src));
const configured = loaded.then(() =>
config.configureCallback ? config.configureCallback() : undefined
);
this.libraries.set(config, configured);
}
return this.libraries.get(config)!;
}
/**
* Get the resource path used to load the application. If the application
* was loaded through a CDN, then this will be the path to CDN resources.
*/
_getLibRoot() {
if (window.STATIC_RESOURCE_PATH) {
return window.STATIC_RESOURCE_PATH + '/';
}
return '/';
}
/**
* Load and execute a JS file from the lib root.
*
* @param src The path to the JS file without the lib root.
* @return a promise that resolves when the script's onload
* executes.
*/
_loadScript(src: string | null) {
return new Promise((resolve, reject) => {
const script = document.createElement('script');
if (!src) {
reject(new Error('Unable to load blank script url.'));
return;
}
script.setAttribute('crossorigin', 'anonymous');
script.setAttribute('src', src);
script.onload = resolve;
script.onerror = reject;
document.head.appendChild(script);
});
}
}
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