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.

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.

"Completed" is not a standard state of a Promise. The valid states are "Pending," "Fulfilled," and "Rejected." A Promise is initially in the "Pending" state and transitions to either "Fulfilled" or "Rejected" based on the outcome of the asynchronous operation it represents.

The correct option is map. map is used for transforming each element of an array and creating a new array with the transformed values. It is ideal for data transformation tasks in scenarios like an analytics dashboard.

Functional composition allows breaking down complex transformations into smaller, reusable functions. This promotes code modularity, simplifies debugging, and enhances readability by reducing code duplication. It streamlines the development process by composing functions to perform various transformations efficiently. This approach leads to more maintainable and scalable code.

Destructuring assignment is commonly used in React components to handle props and state efficiently. By extracting specific values from the props and state objects using destructuring syntax, developers can improve code readability and make component logic more concise. This practice simplifies the process of accessing and using props and state values within the component, contributing to better-organized and more maintainable React code.

In ES6, enhanced object literals allow dynamic assignment of variables as properties using square brackets. This feature is especially useful when the property name needs to be determined at runtime. It promotes a more flexible and concise way of defining object properties.

To export multiple features from a single module, use export { feature1, feature2 as alias }; where as alias provides an optional alias for the exported feature, making it clear when imported.

The correct option is Event Loop. The Event Loop is a crucial part of JavaScript's concurrency model. It continuously checks the call stack, and when it's empty, it picks up and executes tasks from the callback queue. Understanding the Event Loop is essential for writing efficient and non-blocking code.

Arrow functions do not bind their own 'this' and instead inherit it from the surrounding scope. When used as methods in an object, this can lead to unintended behavior as 'this' will not refer to the object itself, potentially causing bugs.