The text discusses User-Defined Functions (UDFs) in Couchbase, a document database that natively stores data in JSON format. The UDFs are used to extend the capabilities of Couchbase's query language, SQL++. JavaScript is chosen as the most natural way to access and manipulate JSON data due to its popularity among developers. A custom UDF called `traverseTree` is created to traverse a tree structure, such as an organizational hierarchy, using recursion. The UDF takes several parameters and can be defined in different ways, including as a scalar function, inline function with a subquery, or external function. The text also mentions the capabilities of Couchbase's SQL++ UDFs for JavaScript, which were introduced in Couchbase 7.0, and notes that users are encouraged to verify the correctness of any custom code provided in the article.