Transforms

A transform is an instruction that tells Datadance how to derive a field's value. Transforms are written as an array of objects, where each object has a single key (the output field name) and a value (the expression or nested transform).

Structure

Each transform object must contain exactly one key. The key becomes the field name in the output, and the value is either:

1. A string expression evaluated by MozJexl
2. An array of nested transforms for processing sub-objects

Simple expression transforms

Input

{
  "firstName": "Alice",
  "lastName": "Smith",
  "age": 17,
  "price": 100,
  "quantity": 3
}

Output

{
  "firstName": "Alice",
  "lastName": "Smith",
  "age": 17,
  "fullName": "Alice Smith",
  "ageInMonths": 204,
  "isAdult": false,
  "total": 330
}

Transforms

[
  { "fullName": "input.firstName + ' ' + input.lastName" },
  { "ageInMonths": "input.age * 12" },
  { "isAdult": "input.age >= 18" },
  { "total": "input.price * input.quantity" }
]

Expression context

Expressions have access to two contexts:

• input — The original input data object (immutable)
• derived — The accumulated derived state (mutable, starts as a clone of input)

Transform expressions are evaluated in order, so later transforms can reference the results of earlier ones via the derived context:

[
  { "base": "input.price * 1.1" },
  { "total": "derived.base + input.tax" }
]

Expression language

Datadance uses MozJexl as its expression language. It supports:

Category	Operators / Syntax
Arithmetic	+, -, *, /, %
Comparison	==, !=, <, >, <=, >=
Logical	&&, ||, !
Ternary	condition ? trueVal : falseVal
String concat	+
Property access	obj.prop, obj['prop']
Array indexing	arr[0]
Transforms (pipe)	value | transformName(args)