Can someone explain this recursive function MongooseJS
checkIfSlugExists function in your example ensures that there is no documents with slugToFind slug in database already.
checkIfSlugExists not simply checks that the slug if vacant, but it also has some failover mechanisms. So, in the end it returns a promise to a vacant slug:
- If
slugToFinddon't exist in database, then it's returned (line331). - Otherwise
checkIfSlugExistschecks for alongSlug(lines338-341), which is just a longer version of the originalslugToFind. - If both
slugToFindandlongSlugare already taken, thencheckIfSlugExistsstarts adding numbers tolongSlug(line344-355), starting from 2, untill it finds a vacant slug.
Every time checkIfSlugExists wants to check for some new slug it recursively calls itself with this new value.