Consider a scenario where you have a base class for a UI component and multiple derived classes for specific components. How would the constructors and super keyword play a role in initializing state and props?
- Constructors are unnecessary; use default values for state and props.
- Use constructors for state and props initialization without involving the super keyword.
- Employ both constructors and the super keyword to initialize state and props in a structured manner.
- Rely on setter methods to initialize state and props in UI components.
In a scenario with a base UI component class and derived classes, constructors play a crucial role. Utilizing both constructors and the super keyword ensures a systematic approach to initializing state and props, fostering a clear and organized class hierarchy for UI components.
Can JavaScript handle asynchronous tasks natively, and if so, how is this achieved in relation to the event loop?
- Yes, using callbacks.
- Yes, through asynchronous functions and promises.
- No, JavaScript cannot handle asynchronous tasks natively.
- Yes, through synchronous functions.
JavaScript can handle asynchronous tasks through asynchronous functions and promises. The event loop ensures that asynchronous code is executed at the appropriate time.
To rename a named export during import, use the syntax import { originalName as ______ } from 'module-name';.
- newName
- importedName
- aliasName
- renamedName
When importing a named export and giving it a new name, use the as keyword, making option c) aliasName the correct choice. The syntax is import { originalName as aliasName } from 'module-name';.
How does the event loop handle callback functions in JavaScript?
- It executes callbacks immediately when encountered
- It adds callbacks to the call stack for execution
- It delegates callbacks to the message queue for later execution
- It ignores callbacks entirely
The event loop in JavaScript works by constantly checking the call stack and message queue. When the call stack is empty, it picks up tasks from the message queue, including callback functions, and adds them to the call stack for execution. This ensures asynchronous operations are handled in a non-blocking way.
A pure function always returns the same output given the same _________.
- Input
- Output
- Variable
- Function
A pure function is a function where the output is solely determined by its input, making it predictable and easier to test. It always returns the same output for the same input.
JavaScript’s __________ nature allows it to perform non-blocking operations despite being single-threaded.
- Synchronous
- Asynchronous
- Parallel
- Multithreaded
The correct option is Asynchronous. JavaScript's asynchronous nature is a key feature that enables it to handle multiple tasks concurrently without blocking the main thread. This is achieved through mechanisms like callbacks, Promises, and async/await, making it suitable for building responsive and efficient applications.
If you need to access both the index and value in an array using for...of, use __________ to convert the array into an iterable of index-value pairs.
- Object.entries()
- Array.entries()
- indexValuePairs()
- iterable()
If you need to access both the index and value in an array using for...of, use Array.entries() to convert the array into an iterable of index-value pairs. This allows you to destructure the pairs in the for...of loop, providing both index and value in each iteration.
What is the return value when accessing a Map object's element with a non-existing key?
- undefined
- nan
- KeyError
- FALSE
When accessing a non-existing key in a Map, the result is undefined. This behavior is different from objects, where accessing a non-existing property returns undefined.
What character is used to define a template literal in JavaScript?
- Backtick (`)
- Dollar sign ($)
- Hash (#)
- Exclamation mark (!)
In JavaScript, a template literal is defined using the backtick (`) character. It allows for easy string interpolation and multiline strings, making it a powerful feature for string formatting.
When building a new object that combines properties from several sources, how can the spread operator be used effectively?
- Merge properties using the { ...source1, ...source2 } syntax
- Combine properties using the Object.assign() method
- Concatenate properties using the + operator
- Extend properties using the extends keyword
The spread operator (...) is commonly used to merge properties from multiple sources into a new object. Using { ...source1, ...source2 } allows you to create a new object with properties from both sources effectively.
How do generator functions differ from traditional functions in terms of execution?
- Generator functions have multiple entry points
- Generator functions always return a value
- Generator functions are synchronous
- Generator functions have the ability to pause and resume execution
Generator functions differ from traditional functions by having the ability to pause and resume their execution using the yield keyword. This feature enables the creation of iterators and asynchronous programming patterns. Traditional functions, on the other hand, run to completion without the ability to pause.
How do Symbols contribute to better property encapsulation in objects?
- Symbols allow for private properties
- Symbols allow for dynamic property names
- Symbols enforce strict encapsulation
- Symbols are interchangeable with property names
Symbols in JavaScript can be used as unique keys for object properties. This allows for the creation of private properties and better encapsulation, as Symbols are not enumerable in for...in loops and do not clash with other property names.