Middleware
Middleware is a function that operates between the request and response in an application, hence the name “middle-ware.” It sits in the middle and functions between the two.
Manipulation: Middleware can inspect request headers or add specific headers to the response.
- For example, a middleware can check the validity of an authentication token by inspecting the headers.
Adding an intermediate step: Middleware can perform additional actions during request or response processing.
- For instance, a middleware can check the user’s authentication status before accessing a page that requires login, such as a user’s profile or an admin page.
- It can also validate data and send error responses if errors are detected.
Cycle control: Middleware has control over the cycle between the request and the response.
- For example, a middleware can record the time when a request occurs and add it to the response headers.
- It can also perform logging for incoming requests.
How to use Middleware
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app.use((req, res, next) => {
// Code to be executed in the middle
});
next: Calls the next middleware function defined in the stack.- If multiple middleware functions overlap, they will be entered sequentially starting from the first middleware.
- If
next()is not called during the execution of a middleware, the next middleware will not be executed.