How does Promise chaining help in handling asynchronous operations?
- It simplifies callback hell by allowing sequential execution of asynchronous tasks.
- It increases the complexity of asynchronous code.
- It only works with synchronous operations.
- It requires additional external libraries.
Promise chaining is a technique that allows sequential execution of asynchronous tasks, making the code more readable and maintainable by avoiding callback hell.
What happens if a method is called on an object that does not define it but its prototype does?
- The method will throw an error
- The method will be executed using the prototype's implementation
- The method will be executed using the object's implementation
- The method will call the constructor of the object
If a method is called on an object that does not define it but its prototype does, the method will be executed using the prototype's implementation. This is a key feature of prototype-based inheritance in JavaScript.
The __________ loop is used to iterate over the elements of an iterable object in JavaScript.
- for...in
- while
- do...while
- for...of
The for...of loop is specifically designed for iterating over the values of an iterable object, providing a concise and readable syntax for iteration. It simplifies the process of iterating over arrays, strings, maps, sets, and other iterable objects.
ES6 introduces the __________ property in object literals for setting the prototype of the created object.
- Prototype
- proto
- Object.setPrototypeOf()
- Object.create()
In ES6, the proto property in object literals is used for setting the prototype of the created object. It provides a convenient way to establish the prototype chain for an object.
What happens if an error is thrown inside a .then() block in Promise chaining?
- It is automatically caught by the nearest .catch() block in the chain.
- The program crashes with an unhandled exception.
- The error is ignored, and the program continues execution.
- It triggers the global error handler.
If an error occurs inside a .then() block, it will be caught by the nearest .catch() block in the promise chain, preventing it from propagating further and allowing proper error handling.
What is the purpose of the prototype chain in JavaScript?
- To store local variables
- To manage asynchronous operations
- To enable inheritance and method sharing
- To restrict access to certain properties
The prototype chain in JavaScript is crucial for inheritance. When an object is created, it inherits properties and methods from its prototype. This chain allows objects to share functionality and promotes code reusability.
Can Promises help in avoiding callback hell in asynchronous JavaScript code?
- TRUE
- FALSE
- Only in specific cases
- Depends on the browser
Promises play a crucial role in avoiding callback hell in asynchronous JavaScript code. By using promises, you can chain asynchronous operations more cleanly, making the code more readable and maintainable. Option A is correct because Promises are indeed effective in this context.
What distinguishes the Symbol.iterator property in an iterable?
- It uniquely identifies the iterable object
- It defines the iteration logic of the iterable
- It represents the number of iterations
- It is used to check if an object is iterable
In ES6, the Symbol.iterator property is a special symbol used to define the default iterator for an object. The value assigned to this symbol is a function that returns the iterator object, providing the logic for iterating over the object's elements. This allows customizing the iteration behavior for user-defined objects.
In ES6, which method is commonly used as a higher-order function for arrays?
- map()
- concat()
- reduce()
- slice()
The map() method in ES6 is commonly used as a higher-order function for arrays, allowing the transformation of each element with a provided function.
What is tail call optimization in recursive functions and how is it handled in ES6?
- Tail call optimization is a technique where the JavaScript engine optimizes recursive functions to avoid stack overflow errors. In ES6, tail call optimization is not explicitly mandated, but certain engine implementations may provide it.
- Tail call optimization in ES6 can be achieved through the use of proper coding practices, such as making the recursive call the last operation in the function and ensuring no additional processing is performed after the recursive call.
- ES6 introduces the concept of proper tail calls (PTC), allowing some recursive functions to be optimized for tail calls. This optimization is not universally supported across all JavaScript engines.
- Tail call optimization is automatically applied to all recursive functions in ES6, ensuring that stack overflow errors are mitigated, and the recursive calls are optimized for better performance.
Proper tail calls in ES6 involve making the recursive call the last operation in a function. While not all recursive calls benefit from tail call optimization, adhering to PTC principles can enhance performance in situations where tail call optimization is applied.