node-promise-delay-every/README.md

@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.