Dena

Dena is a dead simple scheduler to queue and run async javascript functions.

It turns your async functions into async functions that schedule themselves to use limited resources, so at any given time, only limited number of async tasks are being executed.

Example

Assume you are downloading some URLs, but you need a token to access them. You have limited number of tokens and you can only download one page at a time with one token.

let simulatedDownload = function (delay) {
  return new Promise((acc, rej) => setTimeout(acc, delay))
}

let download = async function (token, path, delay) {
  console.log(`[ ] Started downloading ${path}?token=${token}`);
  
  await simulatedDownload(delay);

  console.log(`[x] Finished downloading ${path}?token=${token}`);
}

You can use Dena, to convert your download function into a smarter download. Dena dynamically assigns a token to your function from a pool of tokens and call your function. Dena assumes the first argument of your function is always the configuration object that needs to be selected from the pool.

let simulatedDownload = function (delay) {
  return new Promise((acc, rej) => setTimeout(acc, delay))
}

let download = async function (token, path, delay) {
  console.log(`[ ] Started downloading ${path}?token=${token}`);
  
  await simulatedDownload(delay);

  console.log(`[x] Finished downloading ${path}?token=${token}`);
}


let tokens = ['1_1a2b3c', '2_4d5e6f', '3_7g8h9i'];
let denaDownload = Dena(tokens, download);

// notice how the first argument is not needed.
// Dena assings a free token to your function dynamically
denaDownload('/one', 1000);
denaDownload('/two', 500);
denaDownload('/three', 2000);
denaDownload('/four', 500); // this waits until /two is downloaded
denaDownload('/five', 100); // this waits until /one is downloaded

/*
  [ ] Started downloading /one?token=1_1a2b3c
  [ ] Started downloading /two?token=2_4d5e6f
  [ ] Started downloading /three?token=3_7g8h9i
  [x] Finished downloading /two?token=2_4d5e6f
  [ ] Started downloading /four?token=2_4d5e6f
  [x] Finished downloading /one?token=1_1a2b3c
  [ ] Started downloading /five?token=1_1a2b3c
  [x] Finished downloading /four?token=2_4d5e6f
  [x] Finished downloading /five?token=1_1a2b3c
  [x] Finished downloading /three?token=3_7g8h9i
*/

Also, each denaDownload return a Promise which gets resolved to download's return value once that instance is executed.

API

Dena(configurationPool, fn);

configurationPool: Array of objects, each element will be fed into fn as its first argument.

fn: async function. fn has to return a Promise, so Dena knows when the execution is done.

Return Value: async fn: Async function that executes fn with dynamically assigned configuration from configurationPool.