Expressions

Expressions in Datadance are written using the MozJexl expression language. They are JavaScript-like expressions that are safely evaluated against the input and derived contexts.

Basic operations

Type	Operators
Arithmetic	+, -, *, /, %
Comparison	==, !=, <, >, <=, >=
Logical	&&, ||, !
Ternary	condition ? valueIfTrue : valueIfFalse
String concat	+

Context variables

• input — The original input data object (immutable)
• derived — The current derived state (mutable, accumulates as transforms execute)

Input

{
  "name": "Alice",
  "price": 50,
  "taxRate": 0.1,
  "age": 20
}

Transforms

[
  { "greeting": "'Hello, ' + input.name" },
  { "total": "input.price * (1 + input.taxRate)" },
  { "status": "input.age >= 18 ? 'adult' : 'minor'" }
]

Output

{
  "greeting": "Hello, Alice",
  "total": 55,
  "status": "adult"
}

Transforms (pipe syntax)

MozJexl uses a pipe | syntax to apply built-in transform functions:

value | transformName(args)

Expression	Result
"hello" | upper	"HELLO"
[1,2,3] | join(', ')	"1, 2, 3"
'42' | parseInt	42

Transforms can be chained:

input.name | lower | capitalize

Custom operators

Datadance adds two custom binary operators:

• _= — Case-insensitive string equality: "Hello" _= "hello" returns true
• === — Strict equality (type + value): "5" === 5 returns false