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transform.script runs a typed TypeScript function in a secure WebAssembly (QuickJS) sandbox. Reach for it whenever a transformation is deterministic but too involved for a LiquidJS template, array map/filter/reduce, multi-step calculations, conditional branching, date arithmetic, or regex parsing.

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When to use Script vs LiquidJS

A good rule: if the logic spans more than two or three lines, use a script.

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The contract

The function must be named script. Its parameter names come from the inputs map, but their order is independent of YAML/JSON key order. Its return-type annotation is this step’s output schema. There is no separate outputSchema: field.
  • Parameter names must equal the configured input keys. Enforced at push time.
  • The : R return annotation is mandatory and is derived to JSON Schema, so downstream steps autocomplete against it. A too-loose annotation (such as unknown) leaves downstream field references unresolvable.
  • No async, import(), or require(), the sandbox has no module loader and the worker calls the function synchronously.

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Example

Here { subtotal, tax, total } is the output schema, so a later step can read {{ steps.calculate-totals.output.total }}.

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Configuration

Configuration goes inside the step’s with: block.
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record<string, string>
Named inputs mapped from template expressions. Keys become function parameters; parameter order is independent of YAML/JSON key order: inputs: &#123; items, taxRate } accepts function script(taxRate: …, items: …): R &#123; … }.
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string
required
TypeScript function declaration. Must be function script(args): R &#123; … } where parameter names exactly match the configured input keys in any order and R is a return type annotation. The annotation IS this step’s output schema.
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number
default:"5000"
Max execution time in milliseconds (default: 5000)
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number
default:"10485760"
Max memory in bytes (default: 10MB)

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Output

Returns unknown. Value returned from script. Validated at runtime against the JSON Schema derived from the function’s return type annotation.