closuresmedium
What is a closure, and where would you actually use one?
Answer
A closure is a function that keeps access to the variables of the scope it was defined in, even after that outer function has returned. Practically it's how you get private state: a counter that owns its own count, a debounce that remembers its timer, or a factory that bakes in configuration. The classic bug it explains is a var loop — all the handlers close over one shared binding, so they all report the final value.
Points an interviewer listens for
- Function + the scope it was created in, retained after return
- Gives private state without a class
- Powers debounce/throttle, memoisation, factories
- Explains the var-in-a-loop bug; let gives a per-iteration binding
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