How do closures impact memory usage in JavaScript, and how can memory leaks be prevented when using closures?
- Closures can increase memory usage as they retain access to their outer function's variables even after the outer function has completed execution. To prevent memory leaks, it's important to ensure that closures don't unintentionally keep references to objects or variables that are no longer needed. One common technique is to nullify references within the closure when they are no longer needed.
- Memory usage in JavaScript with closures can be a concern as closures retain references to their enclosing function's variables, preventing them from being garbage collected. To prevent memory leaks, developers should be diligent about managing references within closures, setting them to null when they are no longer needed.
- Closures in JavaScript can lead to increased memory usage since they capture variables from their parent scope. To prevent memory leaks, it's important to release references in closures explicitly, using techniques like setting variables to null.
- Closures in JavaScript can lead to increased memory usage as they retain references to their enclosing function's variables. To prevent memory leaks, developers should be cautious about what they capture in closures and consider using a memory profiling tool to identify and resolve issues.
Closures and Memory Management
What can be the potential security risks if CORS is not properly implemented?
- Cross-Site Scripting (XSS) attacks
- Server crashes
- Slow page load times
- Improved website performance
If CORS is not properly implemented, it can lead to potential security risks such as Cross-Site Scripting (XSS) attacks. Without proper CORS configuration, malicious websites could make requests to your server from a user's browser, potentially leading to security vulnerabilities. The other options do not directly relate to CORS security risks.
What is the prototype of an object in JavaScript?
- __proto__
- prototype
- base
- parent
In JavaScript, the __proto__ property is a reference to the prototype object that an object inherits from. It is an internal property and can be accessed using object.__proto__. The prototype property, on the other hand, is a property of constructor functions and is used to define the prototype for objects created using that constructor. The other options are not commonly used for this purpose.
You have been tasked with securing a web application against XSS and CSRF attacks. What combination of security headers, practices, and designs would you use to mitigate the risk of these attacks?
- Implement Content Security Policy (CSP) headers and use anti-CSRF tokens.
- Disable browser same-origin policies for enhanced security.
- Store sensitive data in cookies without encryption.
- Allow inline scripts and styles for flexibility.
Option (1) is correct. Implementing Content Security Policy (CSP) headers and using anti-CSRF tokens are effective measures to mitigate XSS and CSRF attacks. Options (2) and (4) are insecure practices that would increase vulnerability. Option (3) is incorrect as sensitive data should be encrypted, not stored in cookies without protection.
What is the primary purpose of indexing in databases?
- Speed up data retrieval
- Reduce storage space
- Enhance data security
- Sort data alphabetically
The primary purpose of indexing in databases is to speed up data retrieval. Indexes provide a quick way to locate specific rows in a large database table, improving query performance. While indexing may use additional storage, its main benefit is optimizing data access.
What are the security implications of using third-party libraries and how can they be mitigated?
- Third-party libraries may introduce vulnerabilities
- Third-party libraries always enhance security
- Third-party libraries have no impact on security
- Third-party libraries only affect performance
Using third-party libraries in software development can introduce security vulnerabilities. These libraries may contain known or unknown security flaws. To mitigate these risks, developers should regularly update libraries to the latest secure versions, use security scanning tools, and perform code reviews to identify and address potential vulnerabilities.
What does the express.json() middleware do in an Express application?
- Parses JSON data from incoming requests
- Sends JSON responses to clients
- Creates a JSON file in the server directory
- Validates JSON data in requests
The express.json() middleware in Express.js is used to parse JSON data from incoming requests. It parses the request body and makes the JSON data available for further processing in your application. The other options do not accurately describe the purpose of this middleware.
How does the Event Loop interact with the Worker Threads in Node.js for handling CPU-intensive tasks?
- The Event Loop directly executes CPU-intensive tasks within its own thread.
- The Event Loop manages CPU-intensive tasks by offloading them to separate Worker Threads.
- The Event Loop blocks until CPU-intensive tasks are completed.
- CPU-intensive tasks are not supported in Node.js.
The Event Loop in Node.js can interact with Worker Threads to handle CPU-intensive tasks. These Worker Threads run in the background, separate from the Event Loop, and can be used to prevent blocking the main thread when performing CPU-intensive operations, such as complex calculations.
Which method would you use to concatenate multiple buffers in Node.js?
- buffer.concat()
- buffer.join()
- buffer.append()
- buffer.merge()
To concatenate multiple buffers in Node.js, you should use the buffer.concat() method. The other options are not valid methods for buffer concatenation.
In Mongoose, how can you ensure data integrity and validate schema definitions for embedded documents?
- Using the required property in the schema
- Using the validate method in the schema
- Using the embedded keyword in the schema
- Using the unique property in the schema
In Mongoose, you can ensure data integrity and validate schema definitions for embedded documents by using the validate method in the schema. This method allows you to define custom validation logic. The required property specifies that a field is required but doesn't validate the schema. The embedded and unique options are not standard Mongoose properties.
In JavaScript, every function has a ______ property that points to the object it was created from.
- object
- constructor
- instance
- funcObj
Every function in JavaScript has a constructor property that points to the object (constructor) it was created from. This property is useful for identifying the constructor function of an object.
Which HTTP header is crucial for handling CORS in web applications?
- Access-Control-Allow-Origin
- Cross-Domain-Allow
- Allow-Access-Control
- Origin-Control-Allow
The crucial HTTP header for handling CORS in web applications is Access-Control-Allow-Origin. This header specifies which domains are allowed to access resources on the server. It plays a central role in configuring the CORS policy for a web server.