How to create a size condition useing AWS dynamodb-mapper-js

I am trying to use the AWS Dynamodb Mapper library with Typescript to update an item in a table depending on the size of an array element (lets call it IDs) of the table.

An issue in the Github repo has been raised for this:

According to the dynamoDB documentation, there is a size operator that we can in a Condition Expression:

I haven't seen any trace of it in the package, is it supported ?

The issue has not been addressed (the DDB documentation cited is here).

I would like the condition to be something like size(IDs) > 12, but FunctionExpression doesn't seem to support this.

How can I use this mapper library to implement a size condition?

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