reuseInFlight.js

/* This is from the ISC licensed async-await-utils project, from here:
   https://github.com/masotime/async-await-utils/blob/master/src/hof/reuseInFlight.js
   Including that quite heavy (due to babel dep) project just for this one function
   is a bit much, so I copy/pasted it here.
*/

const DEFAULT_CONFIG = {
  createKey(args) {
    return JSON.stringify(args);
  },
  ignoreSingleUndefined: false,
};

// for a given Promise-generating function, track each execution by the stringified
// arguments. if the function is called again with the same arguments, then instead
// of generating a new promise, an existing in-flight promise is used instead. This
// prevents unnecessary repetition of async function calls while the same function
// is still in flight.
export default function reuseInFlight(asyncFn, config) {
  config = {
    ...DEFAULT_CONFIG,
    ...(config || {}),
  };

  const inflight = {};

  return function debounced(...args) {
    if (
      config.ignoreSingleUndefined &&
      args.length === 1 &&
      args[0] === undefined
    ) {
      console.warn("Ignoring single undefined arg (reuseInFlight)");
      args = [];
    }

    const key = config.createKey(args);
    if (!inflight.hasOwnProperty(key)) {
      // WE DO NOT AWAIT, we are storing the promise itself
      inflight[key] = asyncFn.apply(this, args).then(
        (results) => {
          // self invalidate
          delete inflight[key];
          return results;
        },
        (err) => {
          // still self-invalidate, then rethrow
          delete inflight[key];
          throw err;
        }
      );
    }

    return inflight[key];
  };
}