tracker_impl_001.js

export default function createTracker(config, context) {
  function addContext(data) {
    const newContext = {...data, _parent: context};
    return createTracker(config, newContext);
  }

  function trackEvent(eventName, payload) {
    // Custom logic for your analytics backend.
    console.log(`tracking event ${eventName}`, {...payload, _parent: context});
  }

  return {trackEvent, addContext, getConfig};
}

tracker_impl_002.js

export default function createTracker(source) {
  const config = typeof source.getConfig === 'function' ? source.getConfig() : source;
  const _parent = typeof source.getContext === 'function' ? source.getContext() : undefined;
  let context;
  let tracker;

  function getConfig() { return config; }
  function getContext() { return context; }

  const setContext = (ctx) => {
    context = _parent ? {...ctx, _parent} : ctx;
    return tracker;
  }

  function trackEvent(eventName, payload) {
    // Custom logic for your analytics backend.
    console.log(`tracking event ${eventName}`, {...payload, _parent: context});
  }

  tracker = {trackEvent, getContext, setContext, getConfig};

  return tracker;
}