无法将图像加载到firebase（Angular）

Question

我使用角度6.我想将图像加载到firebase中。我实现了我的服务来加载图像。但它显示了以下错误，我认为这是由于语句：resolve（upload.snapshot.ref.getDownloadURL（））;

以下是我的服务文件中的代码：

uploadFile(file: File) {
    return new Promise(
      (resolve, reject) => {
        const almostUniqueFileName = Date.now().toString();
        const upload = firebase.storage().ref()
          .child('images/' + almostUniqueFileName + file.name)
          .put(file);
        upload.on(firebase.storage.TaskEvent.STATE_CHANGED,
          () => {
          console.log('chargement...');
          },
          (error) => {
            console.log('Erreur de chargement: ' + error);
            reject();
          },
          () => {
            resolve(upload.snapshot.ref.getDownloadURL());
          }
        );
      }
    );
  }

Here is the error obtained : 

firebasestorage.googleapis.com/v0/b/bookshelves-831b9.appspot.com/o?name=images%2F1529083148026AtoiQuiNesPasEncoreNee.jpg:1 POST https://firebasestorage.googleapis.com/v0/b/bookshelves-831b9.appspot.com/o?name=images%2F1529083148026AtoiQuiNesPasEncoreNee.jpg 400 ()

books.service.ts:79 Erreur de chargement: [object Object]

core.js:1542 ERROR Error: Uncaught (in promise): [object Undefined]
    at resolvePromise (zone.js:814)
    at resolvePromise (zone.js:771)
    at zone.js:873
      at ZoneDelegate.push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:421)
    at Object.onInvokeTask (core.js:3662)
    at ZoneDelegate.push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:420)
    at Zone.push../node_modules/zone.js/dist/zone.js.Zone.runTask (zone.js:188)
    at drainMicroTaskQueue (zone.js:595)