NestJS Is Basically ASP.NET Core, And That's Great!
Not clickbait, I swear. Hear me out. Let's drop some dates first:
ASP.NET 5 was announced in mid-late 2015
ASP.NET Core was RC'ed in January 2016 and released in June 2016.
NestJS 1.0's first NPM publish date was May 14, 2017.
Now that we have the chronological order out of the way, you see why I worded the title the way I did. It's not "ASP.NET Core Is Basically NestJS" because that would infer that NestJS came first -- it did not.
Now that we have the controversy handled, let's look at the similarities and some differences. At the end I'll offer my opinion on when to use one or the other.
Similarities
| ASP.NET Core | NestJS | |
| Controllers | Controllers | Accept incoming HTTP requests and route them to responsible services. |
| Services | Providers | In both frameworks, these can represent repositories, helpers, factories, etc. Services can be dependency-injected into other services and controllers. |
| Namespaces | Modules | In NestJS, modules are meant to organize "closely related set of capabilities". In ASP.NET, Namespaces usually organize by type of class. These are different, but both serve as a way to organize the codebase. |
| Middleware | Middleware | Process request and response objects. |
| Filters | Pipes | Filters in ASP.NET are used for a variety of things, including what NestJS uses pipes for. |
| Filters | Guards | Authorization Filters in ASP.NET are the same as Guards in NestJS. |
| Exception Handlers | Exception Filters | Essentially the same functionality. Convert a thrown exception into a response user can understand. |
| IConfiguration | ConfigModule | App configuration |
| ModelValidation | ValidationPipe | Incoming payload validation |
| ApiVersioning | Versioning | REST endpoint versioning |
| ILogger | Logger | Included logging |
Just looking at the above table, you can see the two frameworks cover all the bases. There are more similarities I have omitted, or this table would get out of control. For example both frameworks support websockets, gRPC, unit testing, graphql, response caching and auth.
Both frameworks use the concept of inversion of control (the D in SOLID) and just generally are very object-oriented. Anyone coming from ASP.NET Core and strongly typed C# would feel right at home in NestJS with TypeScript. It's a natural transition.
Differences
NestJS supports CRON-based tasks. ASP.NET Core's BackgroundTask does not support cron expressions.
NestJS's database ORM support is cool. ASP.NET has EntityFramework which is okay. They're not quite the same thing but do share the same goal -- simplify data access.
NestJS has specific implementations for microservices. ASP.NET supports different transports, but not out of the box.
NestJS supports delegation of long-running or CPU-intensive tasks to queues (Redis-backed) via Bull. It's cool that this is built-in, I don't believe ASP.NET has anything out of the box.
ASP.NET Core's benchmark performance still trounces Node.js, even on Fastify.
Note: It's interesting that out of the popular REST API frameworks, ASP.NET Core is by far the fastest (14) with Fiber (Go) coming in in 34th spot and nothing else in the top 100. Also, these benchmarks don't really matter.
ASP.NET Core's integration testing framework with TestServer is arguably better than anything Jest can offer.
ASP.NET Core has a giant corporation behind it and millions of dollars in resources. NestJS is run by a single guy (not really, but you get the picture).
These differences are largely irrelevant, except, perhaps, for the CRON task support in NestJS. There are Nuget packages which improve BackgroundTasks in ASP.NET Core, but they're not available out of the box.
I'm Starting a Business, Which Should I Use?
As with everything in life, it depends. Do you have a team? What is your team's competency? Do you want enterprise-level support when the time comes? Where will you host?
You can write anything with JavaScript and almost everything with C#. C# developers are going to be a bit more expensive than JavaScript. Hosting C# code is going to be a bit more labor-intensive than anything running on Node and potentially also more expensive. You can deploy a Node app to the edge on CloudFront or Railway for free in a matter of minutes. When you scale and you're running on Node, you'll be piecing together disparate services like Railway, Upstash, Axiom and Clerk. If you're running ASP.NET in Azure, you'll get everything you need in one convenient place and have just one bill to pay (although a higher bill).
Recommendation
If you're bootstrapping a hipster world-altering startup out of your garage, NestJS is the better choice. Assuming you don't need any kind of audit compliance any time soon and you're okay with refactoring later when you join the big leagues.
If you're building something in a regulated industry (aerospace, health, finance), and you're planning to bring in more seasoned and serious engineers who take security and performance seriously, I recommend ASP.NET. There's a reason these huge industries run on enterprise-supported languages like Java and C# and not Node.
You may also consider Gin or Fiber (Golang) if you're writing microservices. If you're writing anything real-time like a game server, you won't be using Node, ASP.NET or Go anyway.
In the end, this is not a very high-stakes choice. Look at the big picture and make the call. You won't be disappointed with either choice!