Which of the following is true regarding object keys in JavaScript?
- Object keys must be unique within an object.
- Object keys can only be of type string.
- Object keys are case-sensitive.
- Object keys can only be integers.
Object keys in JavaScript are case-sensitive. This means that keys with different letter casing (e.g., 'key' and 'Key') are considered distinct in an object. The other options do not accurately describe the behavior of object keys.
How can the async/await syntax be used with error handling mechanisms, like try/catch, to handle asynchronous errors?
- Wrap the entire async function body in a try/catch block
- Use await inside a try/catch block for each individual asynchronous operation
- Use async without try/catch for handling errors
- Use await without try/catch for handling errors
To handle asynchronous errors with async/await, you should use a try/catch block around each individual await operation. This allows you to catch and handle errors for specific asynchronous operations within the async function. Option A would catch errors for the entire function, which might not provide fine-grained error handling. Options C and D are incorrect approaches for error handling with async/await.
When designing a system with high-frequency Read operations, ______ the database can optimize performance by reducing the I/O operations on the database.
- Indexing
- Normalizing
- Caching
- Sharding
In systems with high-frequency Read operations, caching the database can optimize performance by reducing the I/O operations on the database server. Cached data can be quickly retrieved from memory, reducing the load on the underlying database.
You are building an Express.js application where you have to route requests based on the subdomain. What approach would you take to implement this routing behavior?
- Use middleware to parse the subdomain and route accordingly
- Create separate Express.js applications for each subdomain
- Define subdomain-specific routes using regular expressions
- Use query parameters to determine the subdomain
To route requests based on the subdomain in Express.js, the most common approach is to use middleware (Option 1) that parses the subdomain from the request and then routes the request accordingly. This allows for flexibility and maintainability. Creating separate applications for each subdomain (Option 2) can lead to code duplication and complexity. Defining subdomain-specific routes using regular expressions (Option 3) can be error-prone and less maintainable. Using query parameters (Option 4) is not a common or recommended way to handle subdomain routing.
What will happen if there are conflicting names when importing items from a module?
- The last imported item with the conflicting name will override the previous ones.
- An error will occur, and you will need to manually resolve the conflict by renaming the items.
- JavaScript will automatically assign unique names to the conflicting items.
- Conflicting names are not allowed when importing items from a module.
In JavaScript, when you import items from a module, if there are conflicting names (e.g., two imported items have the same name), the last imported item with the conflicting name will override the previous ones. This can lead to unexpected behavior and should be avoided by using unique and descriptive names for imported items.
To run a pre-hook for a custom script named "build," you would define a script named ______ in your package.json file.
- prebuild
- pre-hook
- beforebuild
- pre-build
To run a pre-hook for a custom script named "build" in your package.json file, you would define a script named prebuild. This allows you to execute tasks before the "build" script is run, such as setting up dependencies or configurations. The other options do not follow the standard naming convention for npm pre-hooks.
What is the purpose of the res.send() method in Express?
- To send a response to the client
- To receive data from the client
- To redirect the client to another route
- To render a view template
The res.send() method in Express is used to send a response back to the client. It is commonly used to send text, HTML, JSON, or other data as the response to an HTTP request. It is a fundamental method for responding to client requests in Express applications. The other options are not the primary purpose of res.send().
How can closures be utilized effectively for asynchronous programming in JavaScript?
- Closures are often used in asynchronous programming in JavaScript to capture variables that are needed later when an asynchronous operation completes. This helps in maintaining the context and avoiding callback hell. Closures can be used to create functions that wrap asynchronous operations, making the code more readable and maintainable.
- Closures are commonly used in asynchronous programming in JavaScript to maintain the state and context of a function across asynchronous operations. They can be used to create functions that encapsulate asynchronous logic, making code more modular and readable.
- Closures are a powerful tool in asynchronous programming in JavaScript. They can be used to capture the state and context of a function, allowing asynchronous operations to access and modify variables from their enclosing scope. This is useful for maintaining data integrity and managing complex asynchronous flows.
- In asynchronous programming in JavaScript, closures are often used to capture the state of a function and maintain context across asynchronous operations. This can help in avoiding callback hell and making asynchronous code more readable and modular.
Asynchronous Programming with Closures
How can you extract route parameters in Express.js from a route URL like "/users/:userId"?
- Using req.params.userId
- Using req.query.userId
- Using req.body.userId
- Using req.param.userId
In Express.js, you can extract route parameters using req.params.userId. Route parameters are specified in the URL path with a colon prefix, and you can access them using req.params. The other options are not the correct way to access route parameters.
Using label with break or continue provides more control over which part of the code to ________ or ________ in JavaScript.
- skip, execute
- terminate, run
- jump, skip
- stop, resume
Using labels with break or continue in JavaScript provides more control over which part of the code to skip or execute. Labels allow you to specify which loop or block of code should be affected by break or continue statements when dealing with nested loops or complex control flow.