yet another rate limiting wrapper

README.md

Yet Another Rate-limiting Wrapper

rateLimit(fn[, options])

• fn <Function> Function that will be rate-limited
• options <Object> Configurable options
  • max <number> Maximum number of active instances. Default: 10
  • delay <number> Minimum delay between calls in milliseconds. Default: 10
• Returns: <Function> with the same signature as fn

Example

import { rateLimit } from './rateLimit.js'

const ratedFetch = rateLimit(fetch)

// use .allSettled so that errors don't stop everything
Promise.allSettled([/* URLs to fetch */].map((url) => ratedFetch(url).then((r) => {
  // process response as usual (e.g. `r.json()`)
})).then((results) => console.log('done', results))

rateLimit.js

export default function rateLimit (fn, opts = {}) {
  // delay - minimum milliseconds between calls
  // max - maximum number of running instances
  const { delay = 10, max = 10 } = opts
  let last = 0
  let running = 0
  const queue = []
  return async (...args) => {
    const wait = delay + last - Date.now()
    if (wait > 0) await new Promise((r) => setTimeout(r, wait))
    if (running >= max) await new Promise((r) => queue.push(r))
    ++running
    last = Date.now()
    try {
      return await fn(...args)
    } catch (err) {
      throw err
    } finally {
      --running
      queue.length && queue.shift()()
    }
  }
}

rateLimit.min.js

export default function rateLimit(t,e={}){const a=[],{delay:n=10,max:o=10}=e;let i=0,r=0;return async(...e)=>{const s=n+i-Date.now();s>0&&await new Promise((t=>setTimeout(t,s))),r>=o&&await new Promise((t=>a.push(t))),++r,i=Date.now();try{return await t(...e)}catch(t){throw t}finally{--r,a.length&&a.shift()()}}}