Functions

JavaScript that runs on every event a pipe carries: transform it, filter it out, or enrich it before delivery

On this page

• Function types
• Write a function
• Examples
• Test a function
• Attach a function to a pipe

Function types#

Choose the type when you create a function. It cannot be changed later.

Type	What it does
Transform	Reshapes the event and passes it on.
Filter	Decides whether the event continues. Dropping an event counts as success, not failure.
Enrich	Adds fields to the event without changing what is already there.

Some integrations, such as Zid, install managed functions for you. Your team can add its own next to them.

Write a function#

1. Open Functions and select Write a function.
2. Enter a Name, a Slug (the machine name; it follows the name until you change it) and an optional Description of what it changes and why.
3. Pick the Type.
4. Write the code and select Save function. After saving, only the code can be changed.

A function receives one event and returns it, returns a changed copy, or returns nothing to drop it:

function.jsJavaScript

export default async function (event, { log }) {
  // Return the event you want the next stage to receive
  return event
}

Examples#

JavaScript

// Rename a legacy property before it reaches the warehouse
export default async function (event) {
  const properties = { ...event.properties }
  if (properties.orderId && !properties.transaction_id) {
    properties.transaction_id = properties.orderId
    delete properties.orderId
  }
  return { ...event, properties }
}

JavaScript

// Drop internal test traffic
export default async function (event) {
  const pageUrl = event.context?.page?.url || ""
  if (pageUrl.includes("staging.") || event.properties?.test === true) return
  return event
}

JavaScript

// Tag every event with the store region
export default async function (event) {
  return { ...event, store_region: "us-west" }
}

Test a function#

Once a function is saved, its page runs the code against a sample event. Nothing is ingested and nothing is delivered. Edit the sample event, and the test environment variables, to cover the cases you care about:

event.jsonJSON

{
  "type": "track",
  "event": "purchase",
  "userId": "user_1234",
  "properties": { "transaction_id": "order_98765", "value": 313, "currency": "USD" },
  "context": { "page": { "url": "https://shop.example.com/checkout/thanks" } }
}

Attach a function to a pipe#

Open the pipe and go to its Functions tab. A function runs on every event that pipe carries. Function errors appear in Monitoring under Errors.