/**
 * Copyright 2020 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
 *
 *      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.
 */ /**
 * Keeps track scripts that have been requested by loadScript.
 */ let cachedScripts = { } ; param src export function loadScript ( src ) { const existing = cachedScripts [ src ] ; if ( existing ) { return existing ; } const promise = new Promise < void > ( ( resolve , reject ) => { const script = document . createElement ( 'script' ) ; script . src = src ; script . async = true ; const onScriptLoad = ( ) : void => { resolve ( ) ; } ; const onScriptError = ( ) : void => { cleanup ( ) ; delete cachedScripts [ src ] ; script . remove ( ) ; reject ( new Error ( `Unable to load script ${ src }` ) ) ; } ; script . addEventListener ( 'load' , onScriptLoad ) ; script . addEventListener ( 'error' , onScriptError ) ; document . body . appendChild ( script ) ; function cleanup ( ) { script . removeEventListener ( 'load' , onScriptLoad ) ; script . removeEventListener ( 'error' , onScriptError ) ; } } ) ; cachedScripts [ src ] = promise ; return promise ; } /**
 * Clears the script cache. Used for testing purposes only.
 */ export function clearScriptCache ( ) { cachedScripts = { } ; }