An anonymous function as a handler
Short answer:
It is not possible to remove an event handler if it was declared as an anonymous function.
But let's look at why and what to do about it.
1. Why you cannot remove an anonymous handler
The removeEventListener() method requires the exact same function
that was passed to addEventListener().
Example:
button.addEventListener('click', () => console.log('hi'));
button.removeEventListener('click', () => console.log('hi')); // will not workEvery time you write () => ..., a new function is created in memory.
The browser cannot tell that it is "the same" function, so it does not remove the handler.
2. The correct way - move the function into a separate variable
function handleClick() {
console.log('hi');
}
button.addEventListener('click', handleClick);
button.removeEventListener('click', handleClick); // worksHere handleClick is the same function object,
so removeEventListener can find and remove it.
3. If you really need to remove an anonymous handler
You can save a reference to it in advance:
const handler = () => console.log('hi');
button.addEventListener('click', handler);
// later
button.removeEventListener('click', handler);The key is that handler remains the same function object.
4. If there are many handlers, you can use AbortController
A modern and elegant way:
const controller = new AbortController();
button.addEventListener('click', () => console.log('clicked'), { signal: controller.signal });
// ...later
controller.abort(); // automatically removes the handlerIt works with any functions (even anonymous ones),
because AbortController manages their lifecycle itself.
5. Why this matters
If you do not remove old handlers:
- they can run several times on each click,
- they take up memory (leaks),
- they cause unpredictable behavior when components re-render (in React, for example).
Summary
| Scenario | Can it be removed? | Solution |
|---|---|---|
| Anonymous function | No | Use a named function or save it in a variable |
| Named function | Yes | Pass the same reference |
| Many listeners | Yes | Use AbortController |
| Dynamic removal | Yes | Store functions in a Map/object |
Short Answer
Interview readyA concise answer to help you respond confidently on this topic during an interview.