@joepie91/promise-delay-every

A function for writing one per N amount of time rate-limiting implementations.

When called, it returns a 'delayer' function. This delayer function can be called repeatedly; every time it is called, it returns a Promise that resolves delay milliseconds further into the future. The first time it is called, it resolves immediately.

So for example, if you specify a delay of 2000 milliseconds, the Promise returned from the first call will resolve immediately; the Promise returned from the second call will resolve after 2 seconds, the Promise resolved from the third call will resolve after 4 seconds, and so on.

All of these times are relative to the first call you make - so in the above example, there are 2 seconds between every resolution:

0ms     Call 1
0ms     Resolve 1
2ms     Call 2
3ms     Call 3
5ms     Call 4
2000ms  Resolve 2
4000ms  Resolve 3
6000ms  Resolve 4

If you wait longer than the delay to call the delayer function again, the returned Promise will resolve immediately and that time becomes the new base time for future delays:

0ms     Call 1
0ms     Resolve 1
2ms     Call 2
2000ms  Resolve 2
... time passes, beyond the 2000ms delay ...
7400ms  Call 3
7400ms  Resolve 3
7402ms  Call 4
9400ms  Resolve 4

Example

See also example.js for a runnable version. This example uses Bluebird for Promise.try (read this article to understand why), but Bluebird is not required to use this module.

"use strict";

const Promise = require("bluebird");
const promiseDelayEvery = require("@joepie91/promise-delay-every");

let delayer = promiseDelayEvery(2000);

return Promise.try(() => {
	return delayer();
}).then(() => {
	// Logs immediately after running
	console.log("Hello world 1");

	return delayer();
}).then(() => {
	// Logs 2 seconds after running
	console.log("Hello world 2");

	return delayer();
}).then(() => {
	// Logs 4 seconds after running
	console.log("Hello world 3");
});

API

promiseDelayEvery(delay)

Returns a new delayer function.

• delay: The delay as a number, in millseconds.

delayer()

Returns a new Promise that will resolve at the next scheduled interval, according to the algorithm described at the top of this documentation.

The Promise will never reject.

Changelog

v1.0.1 (February 17, 2020)

• Fixed repository URL in package.json

v1.0.0 (April 23, 2019)

Initial release.