Question: What is a particular performance concern when dealing with event handlers, and how can you cope with it?

1. Finding which element an event occurred on is expensive. Assign most events to document.body and use .is() to act on the element of interest.
2. Some events, such as mousemove and scroll, happen a lot on a typical page. Debounce or throttle their handlers to make sure the handlers are not called more than you actually need.
3. Listening for an event that does not exist can create serious memory leaks. Be careful to spell event names correctly to avoid consuming too much memory.
4. DOM elements with an ID wil fire events more efficiently than with classes. Always use IDs instead of classes where possible.

Answer: The correct answer of the above question is Option B:Some events, such as mousemove and scroll, happen a lot on a typical page. Debounce or throttle their handlers to make sure the handlers are not called more than you actually need.