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This article is about how Nest.js integrates Express loosely in the node framework. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

Node.js provides the http module to listen on the port, process http requests, and return responses, which is what it mainly does.

However, the api of the http module is too primitive, so it is troublesome to process the request response directly based on it, so we will encapsulate it with libraries such as express.

What this layer does is add a lot of methods to request and response to handle request and response, meet the needs of various scenarios, and handle routing, and also provide a call chain of middleware to facilitate reuse of some code. The call chain of this middleware is called the onion model.

But this layer does not solve the architectural problem: what to do when there are more modules and how to manage them? How to divide Model, View and Controller? Wait.

Therefore, when we use Node.js for back-end services, we will package another layer to solve architecture problems. The frameworks of this layer are eggjs (Ant's), midwayjs (Taobao's) and nestjs (foreign ones).

Nestjs is one of the best:

The bottom layer of this layer is still express, koa, etc., which only solves the architectural problems on the basis of those http frameworks.

And nestjs also does a particularly good job, it does not rely on any http platform, it can be flexible to switch.

So how does nestjs switch between the underlying platforms?

Think about how react can render vdom to canvas, dom, native?

Define a unified layer of interfaces, which are implemented by the render logic of various platforms. This pattern is called the adapter pattern.

The adapter pattern is that when a function implemented by a third party is used, it does not depend on it directly, but defines a layer of interface for the third party to adapt to it. In this way, any scheme adapted to the interface of this layer can be integrated and can be switched flexibly.

Nest.js provides a layer of HttpServer to the underlying http platform, defining a bunch of methods used:

Because the interface of ts must implement all the methods, in order to simplify, it inherits a layer of abstract class AbstractHttpAdapter, which defines the methods to be implemented as abstract.

Then express or other platforms such as fastify can connect to Nest.js as long as they inherit the adapter's class and implement the abstract methods in it:

For example, ExpressAdapter:

Or FastifyAdapter:

The logic is in the platform-express and platform-fastify packages, respectively:

The first line of Nest.js is to call create:

In create, a httpAdapter is selected to create the service:

The default is express:

In this way, the methods of request and response that are called later will eventually be express.

For example, in controller, you can use the @ Request decorator to inject reqeust objects, and you can call various methods of reqeust.

Import {Controller, Get, Request} from'@ nestjs/common';@Controller ('cats') export class CatsController {@ Get () findAll (@ @ Request () request: Request): string {return' This action returns all cats';}}

If you want to call some platform-specific methods outside of the interface, and Nest.js also supports it, use @ Req instead to inject:

Import {Controller, Get, Req} from'@ nestjs/common';@Controller ('cats') export class CatsController {@ Get () findAll (@ @ Req () request: Request): string {return' This action returns all cats';}}

This injects a native request object for a specific platform, such as express, and you can use all its methods directly.

In addition, if you really want to use a specific api of the Express platform, you can specify the corresponding type parameters when you NestFactory.create, so that you can do the corresponding type hints and checks:

But this is coupled to a specific platform, which is not recommended unless it is certain that the platform will not be switched.

This is what the http platform does, and so is the websocket platform:

A unified layer of interface is defined, which is connected to socketio and websocket respectively by adapter, which can be flexibly switched:

Illustration of Nest.js 's processing of http and websocket platforms:

Thank you for reading! This is the end of the article on "how to loosely couple Nest.js in the node framework to integrate Express". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, you can share it out for more people to see!

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