In the method myArray.map(callback), what is the second argument passed to the callback?
- Element's Index (optional)
- Current Array (optional)
- Previous Element (optional)
- Current Index (optional)
In the map() method, the second argument passed to the callback is the current array itself. While the first argument represents the current element, the second argument provides access to the entire array if needed for mapping logic.
During code review, you notice a function defined as an expression is being invoked before its definition in a set of sequential scripts. What might be a potential risk in this scenario?
- The function may not have access to outer variables.
- The function may throw a TypeError when invoked.
- The function may have undefined behavior.
- The function will work without any issues.
In JavaScript, when a function expression is invoked before its definition, it may result in undefined behavior. This is because the function's declaration is not hoisted to the top of its scope like function declarations, and it may not have access to variables declared after its invocation.
Which method creates a new array with all elements that pass a test implemented by the provided function?
- reduce()
- forEach()
- filter()
- find()
The filter() method creates a new array with all elements that pass the test implemented by the provided function. It's a non-mutating method, meaning it doesn't change the original array. In contrast, reduce(), forEach(), and find() serve different purposes.
You are refactoring a codebase and converting regular functions to arrow functions. In which of the following cases would you need to be most cautious about changing the function type due to the "this" keyword's behavior?
- When the function is used as an event handler
- When the function is a method in a class or object
- When the function uses "let" instead of "var"
- When the function is used for mathematical operations
When converting regular functions to arrow functions, you need to be cautious when the function is a method in a class or object. Arrow functions do not have their own "this" binding and instead inherit it from their enclosing scope. This can lead to unexpected behavior in object methods if "this" is used within the function. In other cases, such as event handlers or simple functions, arrow functions may be safely used.
What is the main difference between stopPropagation and stopImmediatePropagation?
- stopPropagation stops the event from further propagation but allows other event listeners on the same element to execute.
- stopPropagation prevents default behavior in addition to stopping propagation.
- stopImmediatePropagation stops further propagation and prevents other event listeners on the same element from executing.
- stopPropagation is used for touch events, while stopImmediatePropagation is used for mouse events.
stopPropagation and stopImmediatePropagation are methods used to control event propagation. The main difference is that stopPropagation stops further propagation but allows other event listeners on the same element to execute. In contrast, stopImmediatePropagation not only stops further propagation but also prevents other event listeners on the same element from executing, even if they are in the same event phase. This can be useful when you want to ensure that certain listeners are not triggered.
You are debugging a JavaScript application and notice that the call stack refers to an anonymous function, making it difficult to trace the error. What could you do to make future debugging easier without altering the function's behavior or structure significantly?
- Convert the anonymous function into a named one
- Use a breakpoint in the browser's debugger
- Add more comments to the anonymous function
- Change the code structure to eliminate the function
To make future debugging easier without altering the function's behavior significantly, you can convert the anonymous function into a named one. Giving a function a meaningful name can help you identify it more easily in the call stack and error messages, making debugging less challenging. Renaming the function doesn't alter its behavior or structure but enhances code readability and maintainability.
To prevent an infinite loop, you should always modify the ________ variable inside a while loop.
- condition
- counter
- iterator
- sentinel
To prevent an infinite loop in a 'while' loop, you should always modify the 'counter' variable. This ensures that the loop will eventually terminate when the condition becomes false, preventing it from running indefinitely.
You encounter a bug in your code where the wrong block of code is being executed despite the condition being false. What could be a possible reason for this?
- Logical operator precedence
- Syntax error
- Variable scope
- Type coercion
One possible reason for the bug could be incorrect logical operator precedence. If the operators are not used in the right order, it can lead to unexpected results. Understanding operator precedence is crucial to avoid such issues and ensure that conditions are evaluated as intended.
Which of the following HTTP methods does NOT have a body in the Fetch API?
- GET
- POST
- DELETE
- PUT
In the Fetch API, the HTTP GET method does not have a body because it is used to retrieve data from a server. The other methods like POST, DELETE, and PUT can include a request body to send data to the server. Understanding this is essential when working with APIs for data retrieval and manipulation.
What is the main purpose of using asynchronous programming in JavaScript?
- Improved Performance
- Simplifying Code
- Avoiding Errors
- Synchronous Execution
The main purpose of using asynchronous programming in JavaScript is to improve performance. It allows tasks like network requests, file operations, and timers to be executed without blocking the main thread, resulting in a more responsive and efficient application. This is especially crucial in web development.