Upload V3

// V1: Mensur
public uploadImage(): Promise<void> {
    // File for Upload
    const targetPath: string = this.pathForImage(this.lastImage);
    const reader = new FileReader();
    return new Promise<void>((resolve, reject): void => {
        this.file.resolveLocalFilesystemUrl(targetPath)
            .then(entry => (<FileEntry>entry).file(file => {
                reader.onloadend = (): void => {
                    const imgBlob = new Blob([reader.result], { type: file.type });
                    this.uploadXHR(imgBlob).then(
                        () => resolve(),
                        () => reject()
                    );
                };
                reader.readAsArrayBuffer(file);
            }))
            .catch(err => console.warn("'AvatarProvider.uploadImage()'", err));
    });
}

// V2: Better promise
public uploadImage(): Promise<void> {
    const targetPath: string = this.pathForImage(this.lastImage);
    const reader: FileReader = new FileReader();

    let file: File = null;

    return this.file
        .resolveLocalFileSystemUrl(targetPath)
        .then((entry: FileEntry) => new Promise<void>((resolve) => {
            entry.file((loadedFile: File): void => {
                file = loadedFile;

                reader.readAsArrayBuffer(file);
                reader.onloadend = resolve;
            }
        ))
        .then(() => new Blob([reader.result, { type: loadedFile.type }]))
        .then((imgBlob: Blob) => this.uploadXHR(imgBlob))
        .catch((error: Error) => console.warn("AvatarProvider.uploadImage()", 'Error while uploading image', err));
}

// V3: Async / await (best)
public async uploadImage(): Promise<void> {
    try {
        const targetPath: string = this.pathForImage(this.lastImage);
        const reader: FileReader = new FileReader();

        const entry: FileEntry = await this.file.resolveLocalFilesystemUrl(targetPath);
        const loadedFile: File = await new Promise<File>((resolve) => {
            entry.file((loadedFile: File): void => {
                file = loadedFile;

                reader.readAsArrayBuffer(file);
                reader.onloadend = resolve;
            }
        });

        const imgBlob: Blob = new Blob([reader.result, { type: loadedFile.type }]);

        return await this.uploadXHR(imgBlob);
    } catch(error) {
        console.warn("AvatarProvider.uploadImage()", 'Error while uploading image', err);
    }
}