Functions

Functions are JavaScript code that runs on every event in transit - between your app and destinations. Use them to filter unwanted events, transform data shapes, or enrich events with external data.

What Functions Can Do

Capability	Example
Filter	Drop bot traffic, test events, internal users
Transform	Rename fields, change event structure, normalize data
Enrich	Add geolocation, company data, or third-party API lookups
Route	Send different events to different warehouse tables

Writing a Function

Functions are JavaScript that receives an event and returns a modified event (or "drop" to filter it out).

Basic Transform

// Rename event properties to match your warehouse schema
function transform(event, ctx) {
  if (event.type === 'track') {
    event.properties.source = event.properties.utm_source;
    delete event.properties.utm_source;
  }
  return event;
}

Filter Events

// Drop events from internal users
function transform(event, ctx) {
  const internalDomains = ['graph8.com', 'yourcompany.com'];
  const email = event.traits?.email || event.properties?.email || '';

  if (internalDomains.some(d => email.endsWith(`@${d}`))) {
    return 'drop'; // magic string — event is discarded
  }
  return event;
}

Enrich with External API

// Add company data from a third-party API
async function transform(event, ctx) {
  const email = event.traits?.email;
  if (!email) return event;

  const domain = email.split('@')[1];
  const resp = await ctx.fetch(`https://api.example.com/company/${domain}`);

  if (resp.ok) {
    const company = await resp.json();
    event.traits.company_name = company.name;
    event.traits.company_size = company.employee_count;
    event.traits.industry = company.industry;
  }

  return event;
}

Strip PII

// Remove sensitive fields before sending to warehouse
function transform(event, ctx) {
  delete event.traits?.phone;
  delete event.traits?.address;
  delete event.properties?.credit_card;

  // Hash email for analytics (keep original for CRM)
  if (event.traits?.email) {
    event.traits.email_hash = ctx.crypto.sha256(event.traits.email);
  }

  return event;
}

Route to Custom Tables

// Send different events to different warehouse tables
function transform(event, ctx) {
  if (event.event === 'purchase') {
    event.JITSU_TABLE_NAME = 'purchases';
  } else if (event.event === 'page') {
    event.JITSU_TABLE_NAME = 'pageviews';
  }
  return event;
}

Available APIs

Functions run in a sandboxed environment with these APIs:

API	Usage	Description
`ctx.fetch(url, options)`	HTTP requests	Call external APIs (enrichment, validation, webhooks)
`ctx.store`	Persistent storage	Key-value store that persists between function calls
`ctx.log`	Logging	Write to Live Events log for debugging
`ctx.geo`	Geolocation	IP-based location data (city, country, region)
`ctx.ua`	User agent	Parsed browser and device information
`ctx.headers`	HTTP headers	Original request headers
`ctx.getWarehouse`	Warehouse queries	Query your data warehouse from within a function
`ctx.source`	Source metadata	Information about the originating stream
`ctx.destination`	Destination metadata	Target destination details

Managing Functions

Go to Connections > Functions in your graph8 dashboard
Click + Create Function
Write your JavaScript in the code editor
Test with sample events using the built-in debugger
Attach to a stream-destination link

Functions include a built-in editor with syntax highlighting and a debugger that lets you test with sample event payloads.

Return Values

Return	What Happens
`event` (modified)	Modified event is sent to destination
New object	Replaces the original event entirely
`"drop"`	Event is discarded (not sent to any destination)
Array of objects	One event becomes multiple events
Nothing	Original event is sent unchanged