Removing document from channels using a channels[] property on the document

As many examples of using the sync function API demonstrate, we are using a channels property on our documents that is investigated by our sync function to determine which channels should be added/removed from the document.

Generally speaking, this works fine, except for the fact that there is no real relationship between the channels property on our document and the actual channels that are part of the document’s sync metadata.

So, for example, if the document contains channel “A” in the channels property, and the sync function does not add the document to channel “A” by not calling the channel() function, then channel “A” still appears in the channels array on the document, even though it is not part of the sync metadata and the document is not really on that channel.

Conversely, if the sync function adds the document to additional channels that were not in the channels property (like internal channels or whatever), then the channels property does not reflect the new channel.

This can be sort of misleading to consumers of the document to know which channels the document is on. We’d have to read the raw content of the document, and then be familiar with the sync metadata structure enough to know which one contains the current set of channels for the document.

Is there any way that the sync function can modify the property of a document so that it remains up to date with the actual channels?

you can not modify document in sync function.
if you want to change channels-documents mapping info ,you can only call channel() function in sync function for specifically changed document.