What is an idempotent operation?

Question

What is an idempotent operation?

Answer 1

A good example of understanding an idempotent operation might be locking a car with remote key.

log(Car.state) // unlocked

Remote.lock();
log(Car.state) // locked

Remote.lock();
Remote.lock();
Remote.lock();
log(Car.state) // locked

lock is an idempotent operation. Even if there are some side effect each time you run lock, like blinking, the car is still in the same locked state, no matter how many times you run lock operation.