Function throttle

Mainly useful on async iterators (for example generated from a stream of events), but see below for other options.

Only throw events at most every x milliseconds.

So when a few events happen quickly in succession, only the first one will be handled, and the next ones will be ignored until enough time (x ms) has passed with the previously handled event.

The second parameter can be used if the timestamps can be calculated from the values on the input iterator (by default Date.now() will be used). This makes it possible to use this operator on synchronous iterators as well!

Example

// imagine a stream of values fired at this pace onto an asyncIterator called itIn:
// 1, wait 5ms, 2, 3, wait 15ms, 4, wait 5ms, 5, wait 5ms, 6wait 10ms, 7wait 5ms, 8

const result = await pipe(itIn, throttle(15), itr8ToArray);
// => [1, 4, 7]

const valuesWithTimestamps = [
   { value: 1, timestamp: 0 },
   { value: 2, timestamp: 5 },
   { value: 3, timestamp: 5 },
   { value: 4, timestamp: 20 },
   { value: 5, timestamp: 25 },
   { value: 6, timestamp: 30 },
   { value: 7, timestamp: 40 },
   { value: 8, timestamp: 45 },
];

// or get the timestamp from the input values
const result = await pipe(
   itr8FromIterable(valuesWithTimestamps),
   throttle(15, ([_v, ts]) => ts),           // throttle with function that gets timestamp from input
   map(([v, _ts]) => v),                     // only keep values
   itr8ToArray,
);
// => [1, 4, 7]