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Showing content from https://reactivex.io/documentation/operators/sample.html below:

ReactiveX - Sample operator

RxJS implements this operator with two variants of sample.

The first variant accepts as its parameter a periodicity, defined as an integer number of milliseconds, and it samples the source Observable periodically at that frequency.

var source = Rx.Observable.interval(1000)
    .sample(5000)
    .take(2);

var subscription = source.subscribe(
    function (x) { console.log('Next: ' + x); },
    function (err) { console.log('Error: ' + err); },
    function () { console.log('Completed'); });

Next: 3
Next: 8
Completed

The second variant accepts as its parameter an Observable, and it samples the source Observable whenever this second Observable emits an item.

var source = Rx.Observable.interval(1000)
    .sample(Rx.Observable.interval(5000))
    .take(2);

var subscription = source.subscribe(
    function (x) { console.log('Next: ' + x); },
    function (err) { console.log('Error: ' + err); },
    function () { console.log('Completed'); });

Next: 3
Next: 8
Completed

There is also a throttleFirst operator, which differs from sample in that it emits the first item emitted by the source Observable in each sampling period rather than the most recently emitted item.

It does not have the variant that uses the emissions from a second Observable to regulate the sampling periodicity.

var times = [
    { value: 0, time: 100 },
    { value: 1, time: 600 },
    { value: 2, time: 400 },
    { value: 3, time: 900 },
    { value: 4, time: 200 }
];

// Delay each item by time and project value;
var source = Rx.Observable.from(times)
  .flatMap(function (item) {
    return Rx.Observable
      .of(item.value)
      .delay(item.time);
  })
  .throttleFirst(300 /* ms */);

var subscription = source.subscribe(
  function (x) { console.log('Next: %s', x); },
  function (err) { console.log('Error: %s', err); },
  function () { console.log('Completed'); });

Next: 0
Next: 2
Next: 3
Completed

sample and throttleFirst operate by default on the timeout Scheduler. They are found in each of the following distributions:

• rx.all.js
• rx.all.compat.js
• rx.time.js (requires rx.js or rx.compat.js)
• rx.lite.js
• rx.lite.compat.js

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