如何使用AWS JavaScript SDK（dynamoDB）处理UnprocessedItems？

I am trying to use an AWS Lambda function to handle events from SendGrid. As I understand it, the event will be an array with a variable number of JSON objects, each representing a given event. I want to write these events to DynamoDB using batchWriteItem and loop the process until I'm not returned any UnprocessedItems. However, I'm getting stuck in an infinite loop. Here is my code now:I am trying to use an AWS Lambda function to ha