could we add leading/trailing edge options for debounce?

[ensconced]

This is more of a feature request than a bug. If you think this feature might make sense then maybe I will raise a PR for it.

Could we add options for debounce to configure whether the saga is called on the leading edge and/or the trailing edge? (Compare to the lodash debounce function).

This would be a very useful feature because by setting leading: true I can ensure I respond immediately to user actions without having to wait for the debounce period to expire.

Perhaps the first delayLength parameter could either be number, or an options object like { delayLength: number; leading?: boolean; trailing?: boolean }?

[Eric Bower]

Hi! Thanks so much for reaching out.

First and foremost: redux-saga is in a stable state and as such backwards compatibility is our primary directive. If you can implement the ability to change debounce -- and throttle -- in a non-breaking way, I'd be happy to review and approve.

• debounce implementation
• throttle implementation

I'm also happy to answer any questions you have.

[ensconced]

I made a start on this. It seems straightforward enough for debounce - my initial attempt at that is here (work in progress) but throttle is a little trickier.

I think the current implementation of throttle would correspond to the leading: true, trailing: true case. For the leading, true, trailing: false case, I think it's as simple as just using buffers.none() instead of buffers.sliding(1)). And leading: false, trailing: false should be simple too (since it basically does nothing).

However, I'm not sure how to approach the leading: false, trailing: true case for throttle.
I wanted to use an fsm like this:

fsmIterator(
  {
    q1() {
      const yActionChannel = { done: false, value: actionChannel(patternOrChannel, buffers.sliding(1)) }
      return { nextState: 'q2', effect: yActionChannel, stateUpdater: setChannel }
    },
    q2() {
      return { nextState: 'q3', effect: yTake(), stateUpdater: setAction }
    },
    q3() {
      return { nextState: 'q4', effect: yDelay }
    },
    q4() {
      // If another action has been received since the leading edge,
      // use that for the trailing edge.
      return channel.isEmpty()
        ? { nextState: 'q5', effect: yTake, stateUpdater: setAction }
        : { nextState: 'q5', effect: yNoop }
    },
    q5() {
      return { nextState: 'q2', effect: yFork(action) }
    },
  },
  needsChannel ? 'q1' : 'q2',
  `throttle(${safeName(patternOrChannel)}, ${worker.name})`,
)

...but channel.isEmpty() is a non-existent method. I'm not sure how to achieve this without some way of checking whether the channel is empty.

[Eric Bower]

Hi! You are welcome to just focus on debounce for now if that makes things simpler for you.