s3UploadObservableWithConcurrency.ts

AWS.config.credentials = {
    accessKeyId: '{accessKeyId}',
    secretAccessKey: '{secretAccessKey}'
};

let bucket: any = new AWS.S3({
    params: {
        Bucket: 'smallorange-local'
    }
});

Observable.from(files)
    .mergeMap((file: IFile) => {
        return Observable.create((subscriber: Subscriber < IFile > ) => {
            bucket.upload({
                Key: file.name,
                ContentType: file.type,
                Body: file,
                ACL: 'public-read'
            }, (err, data) => {
                if (err) {
                    return subscriber.error(file);
                }

                subscriber.next(file);
                subscriber.complete();
            });
        });
    }, null, this.props.concurrency)
    .subscribe(
        (file: IFile) => {
            this.setState({
                files: _.reject(this.state.files, file)
            }, () => {
                toastr.success(`The image ${file.name} was uploaded.`);
            });
        },
        (file: IFile) => {
            toastr.error(`The image ${file.name} could not be uploaded.`)
        }
    );
});