o add elements to an array at a specific index in JavaScript, you would typically use the splice() method. The splice() method allows you to specify the index where you want to add elements and the number of elements to remove (if any). This method can be used for both adding and removing elements at a specific position in an array. For example, myArray.splice(2, 0, 'newElement') would add 'newElement' at index 2 of myArray.

The for...in loop is primarily used for iterating over the properties of an object, not for arrays. It helps access each property name (key) of an object. Attempting to use it with arrays can lead to unexpected results, as it may also iterate over non-index properties added to the array.

Brendan Eich is credited as the main developer behind JavaScript's creation. He created JavaScript while working at Netscape Communications in 1995. His contributions to the language's design and development have had a lasting impact on web development.

The common problem addressed by using asynchronous code in JavaScript is the avoidance of blocking the main thread. Blocking the main thread can lead to unresponsive user interfaces, making the application seem slow or frozen. Asynchronous code helps prevent this issue by allowing non-blocking execution of tasks.

To manage successive data retrieval operations in a clean and maintainable manner, you can use the "Async/Await" approach in JavaScript. Async/Await simplifies asynchronous code and makes it look more like synchronous code, which can significantly enhance code readability and maintainability. It allows you to write asynchronous code in a more sequential style, making it easier to handle multiple asynchronous operations.

CORS (Cross-Origin Resource Sharing) is the API that allows you to make non-simple requests (such as those with custom headers or methods) to another domain in JavaScript while considering the Same-Origin Policy. XMLHttpRequest is an older alternative but has limitations compared to CORS. JSONP is a workaround technique, not an API, and WebSocket is used for full-duplex communication, not for cross-origin requests.

The concept of creating a single function or method that can operate on multiple types of objects is known as "Polymorphism." In JavaScript, polymorphism can be achieved through method overriding and dynamic method binding, enabling different objects to respond to the same method in a way that suits their specific type.

To prevent the browser from freezing during a long-running while loop, you should use asynchronous code and setTimeout to break the loop into smaller chunks. This allows the browser to handle other tasks and prevents the UI from becoming unresponsive. This approach follows the principles of non-blocking and responsive UI in web development.

The correct answer is Promise.race(). This method takes an iterable of promises and returns a new promise that settles as soon as one of the input promises resolves or rejects. It's useful when you want to perform an action as soon as any of several asynchronous tasks completes.

The initial version of JavaScript was created in just 10 days by Brendan Eich in September 1995. This rapid development was possible due to the language's concise design and its primary purpose of enhancing web page interactivity.