Full Stack Interview Questions and Answers- Part 2

Dependency injection is a programming design pattern that aims to decouple a class from its dependencies by separating the process of creating an object from its usage in a program. It involves providing the required dependencies to a class from the outside, rather than having the class create those dependencies itself. This promotes flexibility, modularity, and easier testing by allowing different implementations of dependencies to be injected without changing the class’s code.

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Abstract classes and interfaces are both essential concepts in object-oriented programming, but they serve slightly different purposes.

Abstract classes allow you to define common methods and properties that subclasses can inherit and implement. These classes can also have concrete methods along with abstract ones. Subclasses of an abstract class must provide implementations for its abstract methods.

Interfaces define a contract of methods that implementing classes must adhere to. Unlike abstract classes, interfaces cannot contain concrete methods, only method signatures. A class can implement numerous interfaces, but it can inherit from only one abstract class.

In summary, abstract classes provide a mix of implemented and to-be-implemented methods, while interfaces define a set of methods that must be implemented by classes that use the interface.

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To protect a publicly accessible API from being scraped by bots, you can employ several strategies:

• Implement rate limiting mechanisms to restrict the number of requests an individual IP address can make within a certain time frame. 
• Require users to authenticate or use API keys to access the content. 
• CAPTCHA: Integrate CAPTCHA challenges to differentiate between human users and bots. 
• Analyze the User-Agent header in HTTP requests to identify and block requests 
• Issue tokens that grant temporary access to the API. 
• Render parts of the content dynamically using client-side scripts. 
• Identify and block IP addresses associated with malicious bot behavior. 
• Place hidden links or data fields that are visible only to bots.

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In JavaScript, a callback is a function that is passed as an argument to another function. It allows the provided function to be executed after the completion of a specific task or event.

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Data attributes are attributes added to HTML elements that store extra information or data about the element. They are prefixed with “data-” and can be accessed via JavaScript to provide additional context or metadata.

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CSS resetting removes default styles applied by browsers, providing a clean slate for consistent styling. Normalizing CSS preserves useful default styles while ensuring consistent styles across different browsers by smoothing out differences.

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ACID stands for Atomicity, Consistency, Isolation, and Durability, which are properties ensuring the reliability and integrity of database transactions. These principles help maintain data accuracy and integrity even in the face of failures.

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Blue-Green Deployment involves two distinct environments (blue and green) where one handles live traffic while the other is used for updates/testing. Rolling Deployment, on the other hand, updates instances in a staggered manner without separate environments.

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Design patterns are categorized into three types:

• Creational: Focuses on object creation mechanisms, like Singleton, Factory, and Builder patterns.
• Structural: Deals with the composition of classes and objects, including patterns like Adapter, Decorator, and Facade.
• Behavioral: Addresses how objects interact and communicate, encompassing patterns like Observer, Strategy, and Command.

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Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity by breaking it into multiple related tables. Denormalization, on the other hand, involves combining tables to improve query performance, sacrificing some redundancy for quicker data retrieval.

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The key differences between GraphQL and REST are:

• REST has multiple endpoints for different resources, while GraphQL typically has a single endpoint for all queries.
• GraphQL supports real-time data with subscriptions, while REST relies on techniques like polling. 
• REST uses HTTP methods (GET, POST, PUT, DELETE) for different operations, while GraphQL uses a single endpoint for all operations.

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Here are some common ways to reduce web application load time:

• Compress images and assets to reduce file sizes.
• Optimize and minimize CSS and JavaScript files.
• Use browser caching to store static resources locally.
• Implement content delivery networks (CDNs) for faster content delivery.
• Enable GZIP compression for HTTP responses.
• Minimize HTTP requests by combining resources.
• Prioritize above-the-fold content for quicker rendering.
• Use asynchronous loading for non-essential resources.

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Multithreading is a programming concept in which multiple threads (smaller units of a process) execute independently within the same program. It’s used to improve performance by utilizing multiple CPU cores efficiently and handling concurrent tasks. Multithreading can enhance responsiveness in applications by allowing different tasks to execute simultaneously.

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For successful integration, factors like data quality, extent of customization required, consolidation of integration approaches, future scalability, and the support of top management play crucial roles. Ensuring compatibility, thorough testing, and alignment with business goals are also vital.

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To locate a memory leak, you can use techniques like memory profilers, heap dumps (snapshots of memory state), and verbose garbage collection logs. These tools help identify objects that are not being properly released from memory, which can lead to memory consumption and performance issues.

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Long polling is a communication technique where a client sends a request to the server, and the server holds the request open until new data is available or a timeout occurs. This enables real-time updates without the constant overhead of short polling (frequent requests).

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An application server is a software framework that provides the runtime environment for executing applications and services. It manages tasks like security, transaction management, and resource pooling. It’s often used to host web applications, enabling communication between the application and the web server.

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To test code functionality, you can use tools like:

• Selenium for web application testing.
• WebDriverIO for browser automation.
• Chai, Jasmine, or Mocha for JavaScript testing.
• Karma for running JavaScript tests.
• Nightwatch for end-to-end testing.

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The observer pattern is a design pattern where an object (the subject) maintains a list of its dependents (observers) and notifies them of any state changes, usually by calling one of their methods. This pattern facilitates loose coupling between objects and is used for implementing event handling and real-time updates.