Sessions

Jitsu does not count sessions for every event by default because there is no universal definition of a session that applies to all use cases. Instead, Jitsu provides a flexible way to define sessions using Jitsu Functions. Below is an example function that adds a session_id field to each event:

//adjust as needed, see https://www.npmjs.com/package/parse-duration#available-unit-types-are for available values
const maxInactivityPeriod = '1h'

function randomId() {
    return Math.random(3).toString(36).substring(2) + Math.random(3).toString(36).substring(2);
}

export default async function(event, { log, fetch, store }) {
  const userId = event.userId || event.anonymousId;
  if (userId) {
    const storeKey = `session_id::${userId}`;
    //no anon id means that cookies not working.
    let sessionId = await store.get(storeKey);
    if (!sessionId) {
        //session either expired, or user never had one
        sessionId = `s_${randomId()}`;
        log.debug(`Assigning new session id to ${userId} -> ${sessionId}`);
    } 
    await store.set(storeKey, sessionId, maxInactivityPeriod)
    if (!event.properties) {
        //sometimes the node does not exist
        event.properties = {}
    }
    event.properties.sessionId = sessionId;
  }

  return event;
}