How does throttleTime operator's config parameter work? (ThrottleConfig)

问题

I have read the throttleTime documentation, but I don't get the operator fully.

I know how throttleTime(1000) works. After an event arrives it will skip all subsequent events for 1 second and then start this process again.

What I have trouble to understand is how exactly ThrottleConfig works, which is the third parameter of the operator.

throttleTime<T>(
  duration: number, 
  scheduler: SchedulerLike = async, 
  config: ThrottleConfig = defaultThrottleConfig): MonoTypeOperatorFunction<T>

How do leading and trailing properties change the functionality of the source Observable?

I have read many documentations but they don't clearly explain this.

So there are four options:

1. { leading: true, trailing: false }:
   default option, after receiving event skips other events for specified duration and then repeat.
2. { leading: false, trailing: true }:
   ???
3. { leading: false, trailing: false }:
   Tested this and the Observable doesn't emit anything at all.
4. { leading: true, trailing: true }:
   ???

回答1:

throttleTime will start a new throttle interval (a time period in which no items will be emitted) when it receives a new value and isn't already throttled.

leading and trailing specify whether an item should be emitted at the beginning or end of a throttle interval.

leading: Emit the item that starts a new throttle interval at the beginning of the throttle interval.

trailing: Emit the last item received from the source at the end of a throttle interval.

Visualisation

https://rxviz.com/v/xOvKPypJ

{ leading: true, trailing: false }

source:               --0----1----2----3----4----5----6----7----8-- 
throttle interval:    --[~~~~~~~~~~~~~~~~~]-[~~~~~~~~~~~~~~~~~]-[~~ 
output:               --0-------------------4-------------------8--

{ leading: false, trailing: true }

source:               --0----1----2----3----4----5----6----7----8-- 
throttle interval:    --[~~~~~~~~~~~~~~~~~]-[~~~~~~~~~~~~~~~~~]-[~~ 
output:               --------------------3-------------------7----

{ leading: true, trailing: true }

source:               --0----1----2----3----4----5----6----7----8-- 
throttle interval:    --[~~~~~~~~~~~~~~~~~]-[~~~~~~~~~~~~~~~~~]-[~~  
output:               --0-----------------3-4-----------------7-8--

{ leading: false, trailing: false }

source:               --0----1----2----3----4----5----6----7----8--
throttle interval:    --[~~~~~~~~~~~~~~~~~]-[~~~~~~~~~~~~~~~~~]-[~~
output:               ---------------------------------------------

来源：https://stackoverflow.com/questions/57059666/how-does-throttletime-operators-config-parameter-work-throttleconfig