Bundlers play a key role in tree shaking. They are responsible for analyzing the dependencies between modules, identifying unused code, and removing it during the build process. Common bundlers like Webpack and Rollup are often configured to perform tree shaking to optimize the final bundle size.

The spread operator is limited in deep cloning when dealing with circular references, making it less suitable for complex object structures. Circular references can result in infinite loops during cloning.

"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 reduce method is used to transform an array into a single value by applying a function that accumulates the values of the array. It takes a callback function and an initial value, and iterates over the array, updating the accumulator with the result of the callback function. This is commonly used for summing up values or performing other aggregations.

When using multiple named exports, naming conflicts may arise, leading to increased coupling between modules. It's important to carefully manage naming to avoid issues and maintain a modular code structure.