The fetch function in JavaScript returns a Promise that resolves to the ________ of the request, whether it is successful or not.
- a) Response Object
- b) JSON Data
- c) Status Code
- d) URL
The fetch function in JavaScript returns a Promise that resolves to the Response object of the request, whether it's successful or not. This Response object contains information about the response, including headers and the response body, and allows you to handle the response appropriately.
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.
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.
Which of the following is a correct syntax for an arrow function?
- (param1, param2) => { return expression; }
- function(param1, param2) { return expression; }
- (param1, param2) { return expression; }
- (param1, param2) -> { return expression; }
The correct syntax for an arrow function in JavaScript is '(param1, param2) => { return expression; }'. Arrow functions are known for their concise syntax, especially when there's a single expression to return. The '=>' syntax is used to define arrow functions.
You are debugging a JavaScript application, and you find a variable that seems to be available even after its block has finished executing. What concept of JavaScript allows this to happen?
- Hoisting
- Closure
- Scope
- Shadowing
This behavior is due to the concept of "Closure" in JavaScript. Closures allow functions to maintain access to their lexical scope, even after the outer function has completed execution. This enables the variable to persist and be accessible outside its block.
You're attending a tech conference, and a speaker mentions that JavaScript was initially met with skepticism because of its relation to a more established language. Which language are they referring to?
- Java
- C#
- Python
- Ruby
The skepticism surrounding JavaScript's name is due to its early association with Java. JavaScript was initially named "LiveScript" and was renamed to capitalize on Java's popularity. However, the two languages are quite different in terms of their usage and capabilities.
Which method is used to select an element by its ID in JavaScript?
- getElementByTag
- getElementById
- getElementByClass
- querySelector
The correct method to select an element by its ID in JavaScript is getElementById. This method retrieves an element by its unique ID attribute. The other options do not select elements by their IDs.
In JavaScript, the ________ object represents the eventual
- EventEmitter
- Promise
- Callback
- Observable
In JavaScript, the Promise object represents the eventual completion or failure of an asynchronous operation. Promises are widely used for handling asynchronous tasks, providing a cleaner and more structured way to work with asynchronous code.
In what scenario might a do-while loop be preferred over a while loop, considering best practices?
- When you want to ensure the loop body runs at least once, regardless of the condition.
- When you need to perform a specific number of iterations.
- When you want to optimize loop performance for shorter conditions.
- When you want to break out of the loop early based on a condition.
A do-while loop is preferred when you want to ensure that the loop body runs at least once, regardless of the condition. This is useful in scenarios where you need to perform an action before evaluating the loop condition.
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.
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 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.