froebel/queue.mjs

TypeScript utility library

import noop from "./noop.mjs";
/**
 * Creates a `queue` function that accepts a function as it's only parameter.
 * When `queue` is invoked, the passed in function is executed after the last
 * function passed to `queue` has finished executing. The `queue` function
 * returns the result of the passed in function asynchronously.
 *
 * Reading `queue.done` is `true` if no functions are currently executing /
 * scheduled and otherwise a promise that resolves once the last function has
 * stopped executing and no futher functions are queued.
 *
 * @example
 * ```
 * const queue = createQueue()
 *
 * queue(async () => {
 *   console.log('start a')
 *   await delay()
 *   return 'end a'
 * }).then(console.log)
 *
 * queue(async () => {
 *   console.log('start b')
 *   await delay()
 *   return 'end b'
 * }).then(console.log)
 *
 * queue(async () => {
 *   console.log('start c')
 *   await delay()
 *   return 'end c'
 * }).then(console.log)
 *
 * await queue.done
 *
 * // start a
 * // end a
 * // start b
 * // end b
 * // start c
 * // end c
 * ```
 */

const createQueue = () => {
  let last = null;

  const queued = fun => last = (last ?? Promise.resolve()).catch(noop).then(fun).finally(() => {
    last = null;
  });

  return Object.defineProperty(queued, "done", {
    get: () => {
      var _last;

      return ((_last = last) === null || _last === void 0 ? void 0 : _last.catch(noop).then(noop)) ?? true;
    }
  });
};

export default createQueue;