useThrottle - With continuous inputs, the throttle does not work

[eTallang]

Hi!

I'm using the useThrottle hook, and to me, the implementation of the hook is a bit confusing. My idea of a throttle function, is a function that accepts lots of inputs over time, and outputs the latest value each desired interval.

Say that we input the letters "A" to "G" with a delay of 500ms between each letter, and we throttle it to 2000ms.
This means that the input would be the following (with the delay in parentheses):

• A (0)
• B (500)
• C (1000)
• D (1500)
• E (2000)
• F (2500)
• G(3000)

My assumption is that the output would be A, E and G. A is the initial value, the E should be included since it is emitted 2000ms after the initially accepted value (A), and G should be emitted after 4000ms (since it is 2000ms after the E).
How the useThrottle hook works today, is that it simply starts a new timeout each time a new value is received. This means that the output becomes A and G.

Is the hook wrong (maybe the lastUpdated useRef should have an intial value of Date.now()?), or am I misunderstanding the throttle concept here?

[eTallang]

I think this PR would fix the issue: #273

[luchillo17]

@eTallang If it's working as you say, that's closer to a Debounce, not a throttle (it's not Debounce only because it does send the first value)...

[doughsay]

useThrottle is currently useless as is if what you have is a firehose of changes and you want to throttle it to change at most every delay ms.

The docs say:

By accepting a value and an optional interval, it ensures that the value is updated at most every interval milliseconds.

am I just reading or understanding this incorrectly? If you have a value that is updating every 10ms but you want to throttle it to update every 500ms, then this hook doesn't work... it never fires.