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Lesson 2 Middleware
Objective Describe the function of middleware.

What is middleware?

Middleware is software that connects two otherwise separate applications, enabling software architectures and applications to communicate and operate with one another in spite of being hosted on heterogeneous architectures or platforms. In general, all categories of middleware accomplish the same thing. They provide a set of services that automate the process by which applications communicate. But there different types of middleware. Why? The data and processes in various applications are stored and represented using different techniques. Different types of middleware technologies specialize in providing different types of data or process interoperability. Until there is a middleware tool that integrates everything, companies will continue to combine various tools to meet their specific needs.

Question: What is the function of middleware?
Answer: To connect two otherwise separate applications, enabling software architectures and applications to communicate and operate with one another.

Middleware Categories

These middleware products fall into various categories. The most common middleware categories are:
  1. Message-oriented middleware
  2. RPC systems
  3. Data integration middleware
  4. Distributed object middleware
  5. Transaction processors
  6. Enterprise application integration products
  7. Workflow services

General Middleware Considerations

Throughout this module, we address the pros and cons of each type of middleware. Here, we'd like to raise some overarching considerations that should be raised when you are contemplating the purchase and implementation of any kind of middleware. These considerations include:
  1. In-house expertise
  2. System compatibility
  3. Maintenance

TypeError: Router.use() requires a middleware function

Question: What is meant by "TypeError: Router.use() requires a middleware function but got a Object at Function”.
The error message "TypeError: Router.use() requires a middleware function but got an object at Function" indicates that there is an issue with the code where a middleware function is expected, but instead, an object was passed. In Node.js, middleware functions are functions that have access to the request and response objects and can manipulate them or perform actions on them. The Router.use() function is used to specify middleware functions for the router.
However, in the code where this error occurred, instead of passing a middleware function to Router.use(), an object was passed, which is not a valid argument for this function. This causes the error message to be thrown. To fix this issue, the code needs to be checked to identify where an object is being passed instead of a middleware function to 
Router.use().
The appropriate middleware function should be passed instead, to ensure that the router works as expected.
Middleware Considerations
These general middleware considerations are also available in table form.
  1. In-house expertise: The developers of integration applications are often people whose primary expertise is not in programming but rather in the processes being automated. This is problematic because middleware applications often come with user interfaces that are difficult for programmers and professionals to work with.
  2. System compatibility: Not all middleware fits into standard applications, networks, and systems management product suites. This can make QA and debugging more complex. Some middleware packages have tried to surmount these difficulties, but even they often require workarounds.
  3. Maintenance: Unlike major database and development tools, many middleware packages are not updated in predictable cycles. Integration applications typically incorporate business rules that change constantly. As a result, integration applications must evolve rapidly in ways that are hard to predict, and even harder to maintain.

Middleware Function - Quiz

Click the Quiz link below to check your understanding of the function and types of middleware available and of the issues important to adopting it.
Middleware Function - Quiz
The next lesson is about one type of middleware known as message-oriented middleware.