promise-queue-with-chained-settle-detection

promise-queue-with-chained-settle-detection.js

var bluebird = require('bluebird');
var queue;
var queueLen = 0;

function queueUp(fn) {
  if (!queue) {
    console.log('start');
    queue = bluebird.resolve();
  }
  ++queueLen;
  queue = queue.then(() => {
    return bluebird.resolve(fn()).finally(() => {
      --queueLen;
      if (!queueLen) console.log('done');
      queue = null;
    });
  });
}

queueUp(() => console.log(1));
queueUp(() => bluebird.delay(20).then(() => console.log(2)));
queueUp(() => bluebird.delay(10).then(() => console.log(3)));
setTimeout(
  () => queueUp(() => console.log(4)),
  40
);

/**
 * cdieringer@Snapper-osx:~/node/coinstac-common$ node p-queue.js
 * start
 * 1
 * 2
 * 3
 * done
 * start
 * 4
 * done
 */