Java Script

Java Script (java-script)

Execute embedded JavaScript to transform events.

Transform Scripting Enterprise edition json

Related reference: Scripting Functions.

Discussion

java-script runs one global function for each JSON event in an embedded QuickJS runtime. Define the function named by entry-point (or transform when it is omitted); LyftData calls it as fn(event, ctx). Host helpers are available under ctx.lyft; use the generated Functions reference for their names, signatures, and feature availability.

Return value	Result
The mutated input event object	Replaces the payload.
A new object	Merges its fields with the input according to merge (default unless-exists).
null	Drops the event.
An array	Fans out into multiple events.

The merge setting applies only when the function returns a new object. Mutating and returning the input event replaces the payload instead; it does not apply the merge policy. Time and memory limits are opt-in action settings, and each event gets a fresh JavaScript runtime, so globals do not persist between events; use the host store for cross-event state.

The embedded context does not install fetch or other network access, filesystem access, console, timers, module imports, pipeline variables, or credentials.

Minimal example

actions:
  - java-script: {}

JSON

{
  "actions": [
    {
      "java-script": {}
    }
  ]
}

Contents

• Minimal example

• Execution

• General

• Source

• Schema

A ✓ marks a field that accepts a context variable such as {{ VARIABLE }}.

Execution

Execution

Field	Type	Required	Description
entry-point	string		Name of the exported function to invoke (defaults to transform).
merge	Merge		When returning an object, merge strategy to apply (defaults to unless-exists). Allowed values: overwrite, error, unless-exists
timeout-ms ✓	number (integer)		Maximum wall-clock execution time per event in milliseconds. Examples: 42, 1.2e-10
memory-limit-bytes ✓	number (integer)		Maximum QuickJS heap usage while executing (bytes). Examples: 42, 1.2e-10

General

General

Field	Type	Required	Description
description	string		Short summary shown next to the action in the editor.
condition	lua-expression (string)		Only run this action if the specified condition is met. Examples: 2 * count()

Source

Source

Field	Type	Required	Description
bindings	map (string)		Named string values resolved independently from JavaScript source and exposed through frozen ctx.bindings. Binding/deploy authority is secret-use authority because trusted JavaScript can deliberately reveal a value.
source ✓	lua-expression (string)		Inline JavaScript source. Either source or path must be provided. Examples: 2 * count()
path ✓	file-path (string)		Path (relative to the job workspace) containing the JavaScript source. Examples: /path/to/file, c:\users\joe\data\file.txt

Schema

• Bindings Table
• Merge Options

Bindings Table

Binding	Value
webhook_secret	`${secret

Key format: unknown. Value format: unknown.

Merge Options

Value	Aliases	Name	Description
overwrite		overwrite	Replace fields that already exist on the input event.
error		error	Reject a returned field when it already exists on the input event.
unless-exists		unless-exists	Keep the input value when a returned field already exists.