MarkLogic provides a possibility to see how the given search expression will be processed by the index. XQuery function xdmp:plan is responsible for that - https://docs.marklogic.com/xdmp:plan
The way it works is perfectly described here - https://www.marklogic.com/blog/working-with-xdmp-plan/
My question is if there is JavaScript analog of that function? How can I analyze the queries written in JavaScript?
Sort of depends on what you are doing. But there is probably tooling in this list to match your needs depending on what you are using for your implemntation:
Returns an array of JavaScript objects recording information about how the given search will be processed by the index.
Returns a node representing the query plan of the given SQL SELECT query.
Return a node representing the query plan of the given SPARQL query.
This method returns a representation of the builtin execution plan.