workerable/lib/index.js

A wrapper around SharedWorker to provide a single synced store between browser tabs or windows

'use strict';

var workerUrl = "data:application/javascript;base64,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";

function sharedWritable(init, startTrigger) {
  const worker = new SharedWorker(workerUrl);
  worker.port.start();
  worker.port.postMessage(['init', init]);
  worker.port.addEventListener('message', messageHandler);

  const subs = new Set();
  let stopTrigger = null;
  let data = init;

  function notifyAll() {
    subs.forEach(cb => {
      cb(data);
    });
  }

  function subscribe(callback) {
    callback(data);
    subs.add(callback);

    if (subs.size === 1 && typeof startTrigger === 'function') {
      stopTrigger = startTrigger(set);
    }

    return () => {
      subs.delete(callback);
      if (subs.size === 0 && typeof stopTrigger === 'function') {
        stopTrigger();
        worker.port.postMessage(['close']);
      }
    };
  }

  function set(_data) {
    if (_data === data) return;
    data = _data;
    worker.port.postMessage(['set', data]);
    notifyAll();
  }

  function update(callback) {
    const newData = callback(data);
    if (newData === data) return;
    data = newData;
    worker.port.postMessage(['set', data]);
    notifyAll();
  }
  
  function messageHandler(e) {
    const [type, _data] = e.data;
    if (type === 'set') {
      set(_data);
    }
  }

  return {
    subscribe,
    set,
    update
  };
}

module.exports = sharedWritable;