When comparing a web framework to another, we first need to ask ourselves what problems each framework is trying to solve. After that, we can move on to compare their functionality and choose the one that suits our projects best.
Express was built to help developers with HTTP, not to be a full-stack framework that's packed with features. The framework gives us all the primitives to create all kinds of applications, from simple web applications to hybrid and real-time ones. Unlike big, monolithic frameworks, Express is not packed with things such as ORMs, view helpers, or other complex features. This means that we have the flexibility to plug in whatever we want to.
When starting out with opinionated frameworks such as Rails, we need to learn about their conventions; a few examples of what we need to know are as follows:
Where things go inside the application folder
The naming conventions
How to define data relationships
These conventions can be an advantage for teams with many developers (to keep everybody on the same page), but if we need to create smaller applications or want to avoid the steep learning curve, Express is a better option.
The fact that Express isn't opinionated can be viewed as a good thing or a disadvantage depending on the use case. It's flexible enough that we can create our own conventions, but at the same time, we might not want or have time to do that.
Some frameworks are tied into a particular database or Object Relational Mapper (ORM), but that isn't the case with Express. It doesn't care about how we manage our data, so it doesn't tie us to a database, nor does it include drivers for any.
If we decide to add a database or an ORM to our application, we need to manually include it.
There are a lot of templating engines available for Express, and it's very simple to integrate new ones. Some of them handle layouts and partials so we can reuse code and provide other features.
Express has support for view helpers, but the framework doesn't provide any out-of-the-box support.
Express is a good choice if we want as much control over our applications as possible, without having to recreate basic, HTTP-related functionality over and over again. It adds the bare minimum sugar syntax to create web applications and doesn't force us into using a certain database, ORM, or templating engine.
Since it's a minimalist framework, we can't expect it to have as many features as the more complex frameworks such as Rails, Django, or CakePHP.