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Express.js is a fast, minimalist, and flexible web Application framework for Node.js. It handles routing, middleware, and other web application functionalities, making it the backbone of the back-end in the MEAN stack.

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Node.js follows an event-driven, non-blocking I/O model, which means it uses asynchronous operations and callbacks to handle multiple requests concurrently without blocking the execution of other code.

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Angular CLI (Command Line Interface) is a command-line tool that helps automate various development tasks, such as scaffolding components, generating services, and building the application for production. It simplifies and speeds up the development process.

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Socket.IO is a library that enables real-time bidirectional communication between the client and the server using WebSockets. It allows the server to push data to connected clients instantly, making it ideal for real-time applications.

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Promises are objects that represent the eventual completion or failure of an asynchronous operation. They help in writing cleaner and more readable asynchronous code, avoiding the callback hell problem.

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Angular Directives are markers on a DOM element that tell Angular to attach specific behavior or apply special logic to that element. They can be used for event handling, data binding, structural manipulation, and attribute manipulation.

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You can handle file uploads using middleware such as multer, which simplifies the process of handling multipart/form-data and storing files on the server.

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Data validation can be done using libraries like express-validator, which allows you to define validation rules for request parameters and body data.

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Angular Services are singleton objects that hold business logic and data that need to be shared across components.

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SSR improves the application’s initial loading speed and enhances search engine optimization (SEO).

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Implement authentication and authorization mechanisms, use input validation and sanitization, enable HTTPS, avoid using inline scripts, and protect against cross-site scripting (XSS) and cross-site request forgery (CSRF) attacks.

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NgZone is a service in Angular that enables the execution of code within or outside the Angular zone. Change Detection is a mechanism in Angular that keeps track of data changes and updates the DOM accordingly.

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Lazy loading allows loading modules only when they are required, reducing the initial loading time of the application. To implement lazy loading, use the loadChildren property in the routing configuration.

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PUT is used to update an entire resource, while PATCH is used to make partial updates to a resource.

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Implement pagination by limiting the number of records fetched from MongoDB using limit and specifying the page number using skip.

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Zone.js is a library that helps Angular track and handle asynchronous operations, change detection, and error handling. It enables Angular to know when asynchronous tasks are completed and when to trigger change detection.

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You can use various deployment tools like Docker, PM2, or directly deploy to cloud platforms like AWS, Azure, or Heroku.

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Minify and bundle scripts, enable AOT (Ahead-of-Time) compilation, lazy load modules, and implement server-side rendering.

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AngularJS makes HTTP requests to the Express.js server, which handles these requests through defined routes and returns JSON data. AngularJS/Angular then processes and presents this data on the frontend.

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Express.js, running on Node.js, is well-suited for building RESTful APIs. Express provides functions for handling HTTP methods like GET, POST, PUT, DELETE, etc., which are essential for creating RESTful endpoints. MongoDB’s JSON-like documents make it easy to store and retrieve data in a format that aligns well with RESTful principles.