Transformer

The Transformer block turns the data it receives into a new shape. You can pick and rename fields with a simple map, or switch to JavaScript for anything more involved.

When to use it

• Rename fields to match what another service or your caller expects, like first_name to firstName.
• Keep only the fields you want to send on, and drop the rest.
• Do bigger reshaping in JavaScript: combine fields, turn a list into an object, change every item in a list.
• Don't use it to add or remove items in a list. Use Array Operations.
• Don't use it to make a decision. Use If Condition or Switch.

Inputs

Field	Required	Default	What it does
Field Map	When Use JS is off	empty	Pairs of source field and new name. Each pair copies one field of the input to a field of the new object.
Use JS	No	off	On: ignore the Field Map and build the result with a script instead.
JS	When Use JS is on	empty	The script. The data is available as input, and whatever you return is the result.
Save output to variable	No	off	Store the result in outputs.<name>.

Outputs

Handle	When it is used
Next (right)	Always. The next block receives the new object.

Example

The input is:

{ "first_name": "Avery", "last_name": "Stone", "age": 31 }

With the Field Map:

Source field	New name
first_name	firstName
last_name	lastName

Result (age was not in the map, so it is dropped):

{ "firstName": "Avery", "lastName": "Stone" }

With JS (turn Use JS on):

return { fullName: input.first_name + " " + input.last_name, isAdult: input.age >= 18 };

Result:

{ "fullName": "Avery Stone", "isAdult": true }

How it behaves

• The Field Map builds a brand new object. Only the fields in the map are copied. Everything else is dropped.
• Top-level fields only. The map reads input["first_name"]. It can't reach into address.city. Use JS for nested fields.
• A missing field is left out. If the input doesn't have a mapped field, the new object simply won't have it. It is not an error.
• The map needs an object. If the input is empty (null), the block fails and the Error Handler runs. To reshape a list, use JS, for example return input.map(x => ({ id: x.id }));.
• Use JS wins. With Use JS on, the Field Map is ignored, but it is kept, so you can switch back.
• Script errors fail the block. A script that throws an error triggers the Error Handler.

Related blocks

• JS Runner: run any code, not only reshaping.
• Array Operations: add, remove or filter items in a list.
• Response: its Transform response option reshapes the body right before sending.
• HTTP Request: reshape an API answer before you use it.