James Dunne

Thoughts on software development

13 Sep 2020

MEAN Stack Considered Harmful

The MEAN stack is everywhere.

Proponents promise getting started is easy.

Hundreds of boot camps provide crash courses promising a MEAN stack job. You don’t owe them until you get hired. No win, no fee.

Developers write thousands of words teaching the stack, preaching the benefits. Become a “full stack developer” in as little as twelve weeks.

It’s adored by greenfield developers. They can build new projects fast. And move on even faster.

The MEAN stack is flawed. It is a poor combination of technologies and I consider it harmful.


The ideas underpinning each technology in the stack are fundamentally incompatible, with potential for genuine harm.

The MEAN stack

The acronym used to mean:

  1. MongoDB, a popular NoSQL database
  2. Express, a micro framework for NodeJS
  3. AngularJS, the now-obsolete front end framework
  4. NodeJS, the JS runtime.

Thanks to the JS ecosystem, the A is now a wildcard. Bring your own frontend framework. MERN and MEVN are popular acronyms.

To make life easier, by MEAN I mean any frontend framework. There’s nothing specific to AngularJS here.


“A chain is no stronger than its weakest link” - Thomas Reid

A stack is only as strong as it’s weakest component. MongoDB is that weakest component.

So much has been written about what is wrong with MongoDB as a technology. But I’ll focus on what makes it especially dangerous in combination with other MEAN technologies:

  1. It’s schema-less
  2. It’s unnecessary

The schema-less fallacy

With MongoDB, there is no schema. You’re free to structure your data in response to change. No more heavy migrations. You’re free to iterate fast.

And it works. At first.

You can get up and running with ease. You can change your data structures on the fly, as you build, as requirements change.

It’s a fallacy.

Sure. MongoDB refuses to enforce a schema. But you still get a schema. It’s just on you to enforce it at the application level.

That’s fine. We just need discipline. We just need more unit tests. It’s our fault for being undisciplined.

Bob Martin made this argument for dynamic typing. And it just doesn’t wash.

You still need to design a schema. Otherwise, you end up with a mess of documents with no clear structure. In other words, chaos.

You need to enforce your schema at the application level too. You end up with a patchwork of conditionals, accommodating the two schemas. Or you write a migration to migrate to the new schema.

Someone will screw up eventually. It’s Sod’s law. Instead of failing at the point of error, MongoDB will carry on as normal, letting your application deal with the mess.

It’s no coincidence why popular ODMs come with schema validation. Unfortunately, it’s still at the application level.

If you’re doing all this on a new project with few to no users, what’s the point?

Just use SQL with good integrity constraints. Errors become far more obvious. Data corruptions less common. And that’s crucial in debugging - the last 10% that takes 90% of the time.

It’s unnecessary

Don’t start a project with NoSQL. These solutions solve problems at scale. That was the disclaimer when NoSQL came onto the scene.

MongoDB doesn’t market itself that way. Instead, it pushes itself as solution for problems big and small, as a database for the modern world.

It renders itself unnecessary.

Most applications don’t operate at scale. Your new project, right now, definitely doesn’t.

It’s not just me. The Guardian, despite higher volumes of traffic than most systems, switched to Postgres whilst keeping the car moving (and my news flowing).

Why it’s so prevalent

MongoDB attracts developers because it makes it easy to get something up and running. You have no schema, you don’t need migrations.

That’s great for prototyping. If you can throw it away.

Prototypes often stick around. You’re often forced to shape it up and live with it. That means living with Mongo.

Unfortunately, there’s a subset of developers who only accept new projects. Get something done fast. Move on. They don’t live with their decisions and they never learn from their mistakes.

And there’s another subset, perhaps overlapping, who have been taught the MEAN stack as if it is the way to build software. Twelve week boot camps that promise a development job at the end of it are the culprit. The boot camps don’t have to live with developers trained in a rush.

Why it’s so harmful

MongoDB offers no guarantees on your data. Not even the shape. You’re free to diverge as much as you like. Even nullify whole sub-documents.

Where are those guarantees?

Express doesn’t help. Neither does Node. And if it’s getting to your frontend, your API is broken. End of story.

Nothing in the stack helps guarantee the shape and integrity of the most important part of your application: the data.

Each of these technologies have a number of flaws that make them especially dangerous when combined with MongoDB.

Node + Express + Mongo = quicksand

I remember when Node took the world by storm. There was a huge rush of development in JS, with frameworks, libraries and new ways of building web applications.

Express was one of those frameworks. Express is a lightweight, no frills web framework promising zippy web apps thanks to Node’s non-blocking nature.

Both NodeJS and Express were built before:

  1. Promises entered the mainstream
  2. Static types were seen as a positive

Despite best efforts, it still shows.

There’s no real guarantee that your values are what you expect them to be. Or when you expect them to be, for that matter.

We are then combing that with a DB that offers no remedy and has the same problems. It’s such a great idea, we give it a clever sounding acronym.

You end up with an API built out of quicksand.

Now we’ve got thousand of developers starting new projects thinking this is the standard in full stack JS development. We’ve got thousands more coming in thinking this is the only way.

There are thousands of businesses that depend on the results. And many of them, after the developer has moved on, are left to live with an unreliable and unmaintainable API.

That plus a frontend that’s built on top of quicksand.

Quicksand + SPA = trauma

A frontend framework is apparently a key component of the MEAN stack. It isn’t really. It can be any frontend framework or nothing at all.

On coining, the A stood for “Angular”, which is now “AngularJS”, which was superseded by “Angular”, but could mean anything from React, Vue or just Vanilla JS.

The idea is that the A means an Single Page Application, which consumes the MEN part as an API. So now you have two applications. One made of quicksand and another built on top of it. With a nice wedge of network complexity in the middle.

An SPA adds a layer of complexity and possible failure. They decompose an application into two applications that interact over the network. The complexity makes it harder to debug and maintain the system.

The stack makes debugging harder.

Now you must live with a system that has the complexity of two pieces of software and one of them is a maintainability nightmare.

Is this a good way to build new applications?

Of course not.

Sparing the pain

Step one: stop giving false legitimacy to immature stacks with official-sounding, easy to remember acronyms like MEAN.

Joking. We can’t stop doing this.

Choose a better database

Don’t use Mongo. It’s a disaster.

Instead, stick with boring old tech. You will go a long way with just Postgres or MySQL.

There are good JS solutions for working with SQL databases. Start with those.

Consider static typing

Static types eliminate a whole class of problems by catching invalid use of your data structures at compile time.

That’s exactly what’s wrong with the stack.

Static types are not a replacement for a solid set of tests. But they do stop us from the worst of our stupid errors. Invaluable in a language with two separate null values. Programming is a loser’s game.

Since TypeScript supports gradual typing, you can move over a piece at a time. While you do that, you can start pushing up the strictness.

There are also tools to make the transition easier. AirBnb released one such tool, ts-migrate. But don’t quote me - I haven’t tried it yet.

Implement a full suite of tests

Don’t just rely on unit tests. Test the integration of your subsystems. Test the entire system and the application as a whole.

If you insist on any part of this stack, you need a lot more of this than usual. There is simply more that can go wrong.

There’s no easy way to do this. Writing a good suite of tests means having the right attitude towards testing: tests are mandatory.

Test everything. Use white and black box methods. Start with a good acceptance test and work downwards as you need to.

Integrate components bottom up and test those too. You’ll find more errors at the boundary where components meet.

I recommend reading The Art of Testing.

Consider a better framework

There are now solid alternatives to Express. One of those is Nest, built using TypeScript.

Using a framework that was built Promise-first will save you a lot of headache.

Consider a better stack

NodeJS has its problems. Even the guy who built it thinks so.

Deno is a great example of a developer reflecting on their decisions and learning from them.

Don’t use a frontend framework

Unless you need to. Stick with a good old server-rendered templating engine to start with. You’ll get more done faster. And the faster you release, the better the outcomes.

Closing thoughts

Ditching Mongo is the best thing you can do for a project. Everything is an order of magnitude easier once you do that.

A stack is only as strong as it’s weakest component. Even if it’s part of an easy to remember acronym. Mongo is the weakest link.

Stop using Mongo, start living.