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node_modules
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# @joepie91/promise-delay-every
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A function for writing *one per N amount of time* rate-limiting implementations.
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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.
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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.
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All of these times are relative to the first call you make - so in the above example, there are 2 seconds between every resolution:
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```
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0ms Call 1
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0ms Resolve 1
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2ms Call 2
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3ms Call 3
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5ms Call 4
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2000ms Resolve 2
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4000ms Resolve 3
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6000ms Resolve 4
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```
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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:
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```
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0ms Call 1
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0ms Resolve 1
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2ms Call 2
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2000ms Resolve 2
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... time passes, beyond the 2000ms delay ...
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7400ms Call 3
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7400ms Resolve 3
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7402ms Call 4
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9400ms Resolve 4
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```
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## Example
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See also `example.js` for a runnable version. This example uses Bluebird for `Promise.try` (read [this article](http://cryto.net/~joepie91/blog/2016/05/11/what-is-promise-try-and-why-does-it-matter/) to understand why), but Bluebird is not required to use this module.
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```js
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"use strict";
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const Promise = require("bluebird");
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const promiseDelayEvery = require("@joepie91/promise-delay-every");
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let delayer = promiseDelayEvery(2000);
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return Promise.try(() => {
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return delayer();
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}).then(() => {
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// Logs immediately after running
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console.log("Hello world 1");
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return delayer();
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}).then(() => {
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// Logs 2 seconds after running
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console.log("Hello world 2");
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return delayer();
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}).then(() => {
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// Logs 4 seconds after running
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console.log("Hello world 3");
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});
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```
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## API
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### promiseDelayEvery(delay)
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Returns a new `delayer` function.
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- __delay:__ The delay as a number, in millseconds.
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### delayer()
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Returns a new Promise that will resolve at the next scheduled interval, according to the algorithm described at the top of this documentation.
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The Promise will never reject.
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"use strict";
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const Promise = require("bluebird");
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const promiseDelayEvery = require("./");
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let delayer = promiseDelayEvery(2000);
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return Promise.try(() => {
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return delayer();
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}).then(() => {
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// Logs immediately after running
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console.log("Hello world 1");
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return delayer();
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}).then(() => {
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// Logs 2 seconds after running
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console.log("Hello world 2");
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return delayer();
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}).then(() => {
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// Logs 4 seconds after running
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console.log("Hello world 3");
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});
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"use strict";
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module.exports = function promiseDelayEvery(delay) {
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let lastScheduledEmit = 0;
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return function delayer() {
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return new Promise((resolve, _reject) => {
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let targetTime = lastScheduledEmit + delay;
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let currentTime = Date.now();
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if (currentTime >= targetTime) {
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lastScheduledEmit = currentTime;
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resolve();
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} else {
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lastScheduledEmit = targetTime;
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setTimeout(() => {
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resolve();
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}, targetTime - currentTime);
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}
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});
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}
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};
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{
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"name": "@joepie91/promise-delay-every",
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"version": "1.0.0",
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"main": "index.js",
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"repository": "git@git.cryto.net:joepie91/node-promise-delay-every.git",
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"author": "Sven Slootweg <admin@cryto.net>",
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"license": "WTFPL OR CC0-1.0",
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"devDependencies": {
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"bluebird": "^3.5.4"
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}
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}
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