When comparing MySQL vs MongoDB, the Slant community recommends MongoDB for most people. In the question“What are the best databases to use for Node.js applications?” MongoDB is ranked 5th while MySQL is ranked 6th. The most important reason people chose MongoDB is:
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.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Scalable
MySQL is made to handle a lot of data and to be used in large applications. This makes it extremely scalable and fast, even under a lot of workload.
Pro Multiple third-party tools that help working with MySQL
Since MySQL is one of the most popular relational databases, maybe the most popular, there exist many third-party tools and applications that help developers to use MySQL in their development.
Pro Easy to start working with
Because of it's popularity there are a lot of tutorials and guides out there that help developers install and work with MySQL. The installation process itself is not very hard and there are multiple powerful GUI tools that make it extremely easy to work with MySQL for a beginner.
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 Perfect documentation and tutorials
Miles above other databases in educational resources.
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.
Cons
Con Error messages usually are not very detailed
When you are trying to do something in MySQL and something goes wrong it will simply give you an error message with an error code. Which does not say much about what went wrong unless you look it up online. This can be a little cumbersome during development.
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.
