You're troubleshooting a web application and notice that an event is not being captured during the capturing phase as expected. What could be a potential reason for this event not being captured?
- The event is not properly attached
- The event is not registered
- The event is being canceled by another event
- The event handler is asynchronous
One potential reason for an event not being captured during the capturing phase is that the event is not properly attached to the target element. Capturing phase events need to be registered correctly using methods like addEventListener with the true parameter to enable the capturing phase. Other options may affect event handling but are not specific to the capturing phase.
A do-while loop is particularly useful when you want to ensure the loop body executes at least ________ before checking the condition.
- Once
- Twice
- Never
- Once or more
A do-while loop is useful when you want to guarantee that the loop body executes at least "once" before checking the condition. This is because in a do-while loop, the condition is evaluated after the loop body, ensuring that the code inside the loop executes at least once, even if the condition is initially false.
When a function expression is made async, it returns a ______.
- Promise
- Callback
- Generator
- Class
When a function expression is marked as "async," it returns a Promise. An async function can pause its execution and wait for the Promise to resolve or reject, which is helpful for handling asynchronous operations elegantly.
The _______ pattern is used to create an instance of an object with some default values.
- Factory
- Prototype
- Singleton
- Observer
The Factory pattern is used to create an instance of an object with some default values. It provides an interface for creating objects in a super factory or a factory method. This pattern is commonly used in JavaScript to create objects.
What is the output of the arithmetic expression 7 / 0 in JavaScript?
- 0
- Infinity
- NaN (Not-a-Number)
- Error
The output of the arithmetic expression 7 / 0 in JavaScript is Infinity. In JavaScript, dividing a number by 0 results in positive or negative infinity depending on the sign of the numerator. Attempting to divide by 0 does not throw an error, but it produces infinity.
Which organization developed JavaScript?
- Microsoft
- Mozilla
- Netscape
- Oracle
JavaScript was developed by Netscape. Brendan Eich created it in 10 days in September 1995. While Netscape is best known for its role in the development of JavaScript, it didn't create other popular languages like Java.
What is a potential downside of using async/await syntax?
- It makes code harder to read and understand.
- It can't be used with Promises.
- It always leads to callback hell.
- It reduces code efficiency.
One potential downside of using async/await is that it can make code harder to read and understand, especially for developers who are not familiar with asynchronous programming. It may lead to nested code blocks, which can be challenging to follow. However, when used correctly, async/await can make asynchronous code more readable.
The _______ method is used to handle errors in Promises.
- .then()
- .catch()
- .resolve()
- .reject()
The correct method to handle errors in Promises is the .catch() method. When a Promise is rejected, the .catch() method is called with the reason for the rejection, allowing you to handle and manage errors in your asynchronous code effectively.
You've encountered a "Callback Hell" in a project you've inherited. What could be a strategic approach to refactor and manage the nested callbacks for better readability and maintainability?
- Refactor using named functions
- Continue using nested callbacks
- Use anonymous arrow functions
- Convert callbacks to Promises
When dealing with "Callback Hell," the strategic approach is to refactor the code using named functions. This technique makes the code more readable and maintainable by breaking down nested callbacks into separate named functions. It enhances code structure and comprehensibility, making it easier to manage complex asynchronous logic.
The mechanism of closing over variables is a core concept in ________ programming in JavaScript.
- Functional
- Object-Oriented
- Asynchronous
- Procedural
The mechanism of closing over variables is a core concept in "Functional" programming in JavaScript. Functional programming promotes the use of pure functions and emphasizes the importance of avoiding mutable state. Closures play a vital role in functional programming by allowing functions to capture and remember the surrounding state.
Arrow functions are not suitable for defining _________ functions.
- async
- generator
- anonymous
- recursive
Arrow functions do not work well for defining generator functions. Generator functions use the function* syntax and rely on the yield keyword, which doesn't behave as expected in arrow functions. Therefore, the correct option is generator.
If a variable is declared inside a block using the let keyword, it is not accessible _________ that block.
- Outside
- After
- Before
- Within
If a variable is declared inside a block using the let keyword, it is not accessible outside that block. This is known as block scope, and it helps prevent unintended variable hoisting and leakage. Variables declared with let are limited to the block in which they are defined.