Are all callbacks closures in JavaScript?
Yes. Every callback function closes over the variables from where it was defined. setTimeout callbacks, event listeners, fetch.then, and map/filter/reduce callbacks are all closures.
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More FAQs in Closures in Callbacks and Event Handlers in JavaScript
Because the callback is a closure. It was defined in a scope where those variables existed, so it holds a reference to that lexical environment. When it runs later, it can still access them.
The listener function closes over variables from where it was defined. For example, a click handler can close over a count variable and increment it on each click. The closed-over state persists across events.
Because removeEventListener needs the same function reference that was passed to addEventListener. Anonymous functions create a new reference each time. Use a named function stored in a variable so you can pass the same reference to remove.
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