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Jitsu Server

JavaScript Transform

Use the power of Javascript to modify incoming event object, replace it with a completely new event or produce multiple events based on incoming data.
Also, you can use Transform to assign Data Warehouse specific SQL types for object fields, set the destination table name for each event or to skip the event altogether.


Transform deprecates Mappings. Once Transform is enabled for a destination, all Mappings configs are ignored.

You can use modern javascript language features and built-in functions to transform an incoming event. Jitsu puts incoming event as a global variable: $

Provided javascript must return:

  • single object - modified incoming event or completely new object
  • array of objects - a single incoming event will result in multiple events in destinations
  • null - to skip event from processing

To override the destination table, you need to add a special property named JITSU_TABLE_NAME to the resulting events.

To override the destination SQL column type for a specific object field, you need to add an extra property with the special prefix __sql_type_ added to the name of a field to resulting events. E.g.: __sql_type_utc_time: "date" sets SQL type date for column utc_time

NOTE Jitsu uses Node.js under the hood for JavaScript execution. This requires that node and npm executables are present in $PATH. Furthermore, Jitsu needs node-fetch@2.6.7 and vm2@3.9.9 NPM modules in order to run JavaScript transformations and plugins. These modules are installed in a temporary directory automatically on Jitsu Server startup, but you may set NODE_PATH environment variable with the location of node_modules directory with node-fetch and vm2 installed in order to use pre-installed modules. You can also use our Docker image which is already set up to run JavaScript transformations and plugins.

Server YAML configuration

Transform is controlled via data_layout.transform_enabled and data_layout.transform properties of destination object.


    type: google_analytics
    mode: stream
      transform_enabled: true
      transform: |-
        const context = $.eventn_ctx || $

        return {
            dl: context.url,
            dh: context.doc_host,
            dp: context.doc_path,
            dt: context.page_title,

Modify incoming event

Javascript spread operator allows making a copy of an incoming event while applying some changes in just a few lines of code:

return {...$,
    new_property: $.event_type

Add property to user object:

return {...$,
    user: {...$.user, state: "active"}

Build new event

Collect some user properties to the new object:

return {
    properties: [
            property: "email",
            value: $.user?.email
            property: "language",
            value: $.user_language

Put an original event as a string payload:

return {
    "event_type": "POST event",
    "payload": JSON.stringify($)

Produce multiple events

Produce multiple purchase events from a single shopping cart event:

if ($.event_type == "conversion" && $.products?.length > 0) {
    let results = []
    for (const product of $.products) {
            event_type: "purchase",
            price: product.price
    return results
} else {
    //skip events without any purchase
    return null

Override destination table

Using Javascript spread operator:

return {...$, JITSU_TABLE_NAME: "new_table_name"}

Conventional way:

$.JITSU_TABLE_NAME = "new_table_name"
return $

Override SQL column type

Set simple SQL types:

return {...$, 
    event_date: $.utc_time,                               
    __sql_type_event_date: "date",
    event_time: $.utc_time,
    __sql_type_event_time: "time"

Sql types with extra parameters:

Some Data Warehouses support extra parameters for column types during table creation. For such cases, Transform uses the following syntax to provide data type and column type separately:

return {...$,
    title: $.page_title,
    __sql_type_title: ["varchar(256)", "varchar(256) encode zstd"]

Predefined constants and functions

Transform comes with predefined constants: destinationId and destinationType that can be used to enrich your data

return {...$, 
    destination_id: destinationId,
    destination_type: destinationType,

Also toSegment(event) function is available to set up Segment Compatibility:

return toSegment($)

Using HTTP headers in transformations

Jitsu Server may be configured to enrich incoming HTTP events with HTTP context – headers and possibly other stuff in the future. Please refer to Jitsu YAML configuration section and Jitsu Docker configuration section for more information on enabling the feature.

In order to access HTTP context from JavaScript transformation you may use $context.header() helper function which will return the first header value (if any):

return {...$,
    content_type: $context.header("content-type")

It is also possible to directly access HTTP context via $:

return {...$,
    content_type: $['__HTTP_CONTEXT__'].headers["content-type"][0]