When comparing MongoDB vs CouchDB, the Slant community recommends CouchDB for most people. In the question“What are the best databases to use for Node.js applications?” CouchDB is ranked 5th while MongoDB is ranked 6th. The most important reason people chose CouchDB is:
CouchDB works very well even when the network is physically partitioned
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Perfect documentation and tutorials
Miles above other databases in educational resources.
Pro Great speed
MongoDB queries can be very fast because the data is usually all in one place and can easily be retrieved in a single lookup. But this is true only when the data is truly a document. When it's trying to emulate a relational model it starts to become really slow because it may have to perform many independent queries to retrieve a single document.
Pro Uses JSON
As Node.js uses JavaScript there's no need to map the returned JSON data from MongoDB, as JavaScript is a superset of JSON. Essentially solving object-relational impedance mismatch by its very nature. Working with JSON is also easier overall as it more easily fits into how you would represent data on the client.
Pro Doesn't require a unified data structure
Mongo is very flexible in that it doesn't require a unified data structure across all objects. So it's rather easy to use.

Pro Easy to scale
MongoDB has powerful sharding and scaling capabilities for when the data stored in the database gets so large that a single machine may not be able to store all of it. Sharding solves this problem through horizontal scaling. Mongo gives developers the ability to easily and painlessly add or remove as many machines as needed.
Pro Works well between physical network partitions
CouchDB works very well even when the network is physically partitioned
Pro Available
CouchDB is considered an available DMS according to the ACP theory of database management. As such it allows every client to always read and write
Pro Useful for applications where versioning is important
CouchDB is mostly used in applications where a large amount of data needs to be accumulated and where data only changes rarely.
Pro Changes API
You can use the RESTful API to listen for changes in your database, which is something most databases can't do. It makes it really easy for clients to keep their view of data up-to-date.
Pro RESTful API
Since everything is stored as a JSON document and served over HTTP, it's perfectly suited for communicating with client-side javascript, with or without middleware.
Cons
Con Reported to lose or corrupt data
MongoDB is famously known for leaking and losing data over time.
Con Document Stores may be not suited for relational data
MongoDB has no JOIN, all relations are supposed to be resolved client-size which entails additional requests to the server.
Con Need many search features
Though it is possible to index and search text in documents in MongoDB 4.0 in multiple languages. The indexing and search is not as powerful as for example Elastic Search. For instance not being able to search for only parts of words.
Con Can only achieve consistency through replication and verification
Since CouchDB is considered an AP (Available, Partition-Tolerant database management system), it is not really consistent (not all clients can have the same view of the data consistently) and the only way to achieve some "eventual consistency" is through replication and verification of data.
Con Uncertain future
After a very promising start, development began to drag after major supporters like Canonical, Selenium and CouchOne either shut down or moved to other tools. Development has begun to pick up again.
