Update 2012-12-05
There is now an official AWS SDK for Node.js, see the introductory post AWS SDK for Node.js - Now Available in Preview Form for details, here are the initially supported services:
The SDK supports Amazon S3, Amazon EC2, Amazon DynamoDB, and the
Amazon Simple Workflow Service, with support for additional services
on the drawing board. [emphasis mine]
Update 2012-02-27
Wantworthy has implemented a Node.js module for accessing Amazon DynamoDB a week after its launch date, thus covering 2) as well, see dynode:
Dynode is designed to be a simple and easy way to work with Amazon's
DynamoDB service. Amazon's http api is complicated and non obvious how
to interact with it. This client aims to offer a simplified more
obvious way of working with DynamoDB, but without getting in your way
or limiting what you can do with DynamoDB.
Update 2012-02-11
Peng Xie has implemented a Node.js module for accessing Amazon DynamoDB at its launch date basically, thus covering 2) already, see dynamoDB:
DynamoDB uses JSON for communication. [...] This module wraps up the request
and takes care of authentication. The user will be responsible for
crafting the request and consuming the result.
Unfortunately there is no official/complete JavaScript SDK for AWS as of today (see AWS Software Development Kits and boto [Python] for the available offerings).
Fortunately decent coverage for several AWS services in JavaScript is provided by the Node.js library aws-lib already though, which would be a good starting point for adding DynamoDB accordingly. An as of today unresolved feature request to Add support for DynamoDB has been filed already as well.
Further, AWS forum user gmlvsk3 has recently implemented dedicated JavaScript interface for DynamoDB, but supposedly you need [a] Java runtime to run it, because it is based on the Mozilla Rhino JavaScript engine - I haven't reviewed the code in detail yet (at first sight it looks a bit immature though in comparison to e.g. aws-lib, but may cover your needs regardless of course), so you should check it out yourself.
Finally, you can implement JavaScript HTTP Requests to Amazon DynamoDB yourself of course (see the API Reference for Amazon DynamoDB for details):
If you don't use one of the AWS SDKs, you can perform Amazon DynamoDB
operations over HTTP using the POST request method. The POST method
requires you to specify the operation in the header of the request and
provide the data for the operation in JSON format in the body of the
request.