Minimal async/await Rate Limiter

Super simple promise-based Rate Limiter:

• comes in at 9.058 bytes and zero dependencies
• fully typed
• maintains in-order execution and supports priorities
• constant O(1) runtime, no matter the queue length or priorities

Installation

npm install priority-limiter --save

Usage

Simply import, then create a new Limiter Instance. The first parameter describes how many request are allowed within the timeframe of the second paramter (in seconds).

For example, allow 5 requests per 10 seconds:

import Limiter from "priority-limiter";

const limiter = new Limiter(5, 10);

(async () => {
	while (true) {
		await limiter.awaitTurn();

		//do requests...
	}
})();

The default priority is 0. Higher priorities will execute before lower ones. Requests with the same priority are resolved in-order of function calling.

await limiter.awaitTurn(1); //priority 1, will execute before default priority 0.

Lastly, you can specify the maximum duration a request can wait for their turn. Promise will reject when waiting longer:

try {
	await limiter.awaitTurn(0, 30); //timeout if waiting for longer than 30 seconds.
} catch (err) {
	console.log(err); //on timeout: "Limiter timed out."
}

Documentation

new Limiter(request_number, per_seconds)

• request_number {Number} How many elements will resolve per seconds_number seconds.
• per_seconds {Number} How long the timeframe for request_number is in seconds. Defaults to 60.

Creates a new Limiter Instance.

awaitTurn([priority, timeout])

• priority {Number} Elements with higher priority will resolve before elements with lower priority. Defaults to 0.
• timeout {Number} Reject if element waits for longer than this many seconds. Defaults to 0 (never rejects).

Resolves once ready. Use await to wait until you can continue.

getLength()

Gets the current queue length, i.e. how many calls to awaitTurn() have not been resolved yet.

isEmpty()

Checks whether the queue is empty, i.e. if there are no calls to awaitTurn() that have not been resolved yet.

getUsedResolves()

Get how many calls to awaitTurn() have already been resolved within the last per_seconds seconds (thus another request_number - getUsedResolves() calls can be made right now).

getTimeTillNextResolve()

Get how long it will be until the next call to awaitTurn() will resolve in seconds.

License

MIT