Initial commit

.gitignore

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+yarn.lock
+node_modules

README.md

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+# @joepie91/promise-delay-since
+
+A function that, when called, produces a Promise that resolves a specified amount of milliseconds since a particular timestamp - or immediately, if the delay since that timestamp has already passed.
+
+This is particularly useful when implementing rate-limiting and/or task distribution code - your implementation only has to track the timestamp of the last call, and leave it up to this module to decide when to resolve a Promise that kickstarts the next task.
+
+## Example
+
+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.
+
+```js
+"use strict";
+
+const Promise = require("bluebird");
+const promiseDelaySince = require("@joepie91/promise-delay-since");
+
+let startTimestamp = Date.now();
+
+Promise.try(() => {
+	// Logs immediately after running
+	console.log("Hello world 1");
+	
+	return promiseDelaySince(startTimestamp, 2000);
+}).then(() => {
+	// Logs 2 seconds after running
+	console.log("Hello world 2");
+	
+	return promiseDelaySince(startTimestamp, 3000);
+}).then(() => {
+	// Logs 3 seconds after running
+	console.log("Hello world 3");
+});
+```
+
+## API
+
+### promiseDelaySince(sinceTimestamp, delay)
+
+Creates a new Promise that will resolve `delay` milliseconds from the specified `sinceTimestamp`. If the current time is later than `sinceTimestamp + delay`, the returned Promise will resolve immediately.
+
+- __sinceTimestamp:__ The reference timestamp to start counting from, as a 'UNIX timestamp' in milliseconds (like you get from `Date.now()`).
+- __delay:__ The delay as a number, in milliseconds.
+
+The Promise will never reject.

example.js

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+"use strict";
+
+const Promise = require("bluebird");
+
+const promiseDelaySince = require("./");
+
+let startTimestamp = Date.now();
+
+Promise.try(() => {
+	// Logs immediately after running
+	console.log("Hello world 1");
+	
+	return promiseDelaySince(startTimestamp, 2000);
+}).then(() => {
+	// Logs 2 seconds after running
+	console.log("Hello world 2");
+	
+	return promiseDelaySince(startTimestamp, 3000);
+}).then(() => {
+	// Logs 3 seconds after running
+	console.log("Hello world 3");
+});

index.js

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+"use strict";
+
+module.exports = function promiseDelaySince(previousTimestamp, delay) {
+	return new Promise((resolve, reject) => {
+		let targetTime = previousTimestamp + delay;
+		let currentTime = Date.now();
+
+		if (currentTime > targetTime) {
+			resolve();
+		} else {
+			setTimeout(() => {
+				resolve();
+			}, targetTime - currentTime);
+		}
+	});
+};

package.json

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+{
+  "name": "@joepie91/promise-delay-since",
+  "version": "1.0.0",
+  "main": "index.js",
+  "repository": "git@git.cryto.net:joepie91/node-promise-delay-since.git",
+  "author": "Sven Slootweg <admin@cryto.net>",
+  "license": "WTFPL OR CC0-1.0",
+  "devDependencies": {
+    "bluebird": "^3.5.4"
+  }
+}