Function syntax - Snag Docs

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Overview

To maintain consistency and security, all Stratus functions are validated before they are saved. This guide explains the required syntax, module restrictions, and best practices to help you create functions that pass validation.

Module Export & Handler Function

Single Handler Export

Your code must export exactly one handler function.

Exporting multiple handler definitions or not exporting a handler at all will cause validation to fail.

// ❌ Incorrect – no exported handler:
const handler = async (input, output) => { ... };

Proper Export Format

Always export your handler as a property of module.exports.

// ✅ Correct:
module.exports.handler = async (input, output) => {
  // Function body...
}

The exported handler must be a function. Assigning non-function values (e.g., a string) will trigger an error.

Handler Function Parameters & Behavior

Parameter Requirements

The handler function must accept exactly two parameters:

input – holds input data
output – provides methods for setting and building the function’s output

module.exports.handler = async (input, output) => { ... };

Using output.setResult

Inside your handler, you must call output.setResult to set the result object.

// ❌ Incorrect:
module.exports.handler = async (input, output) => {
  // Missing call to output.setResult
  return output.buildOutput()
}

Calling output.buildOutput()

The handler must return the result of output.buildOutput(). Omitting this call is not allowed.

// ✅ Correct:
module.exports.handler = async (input, output) => {
  output.setResult({ message: 'Hello' })
  return output.buildOutput()
}

If the handler does not accept exactly two parameters, validation will fail with a message similar to: “The ‘handler’ function must accept exactly two parameters: ‘input’ and ‘output’.”

Module Import Requirements

Allowed Modules

You may include external modules via require(), but only approved packages are allowed:

axios
lodash
viem and its approved subpath viem/chains

const axios = require('axios')

Disallowed Modules

The following are not allowed:

Modules not on the approved list (e.g., Node’s fs)
Unapproved subpaths from approved packages
Dynamic requires (using variables for module names)

// ❌ Incorrect:
const mod = 'axios'
const axios = require(mod) // Dynamic require not allowed

Extra Exports

Adding extra properties to module.exports (aside from the handler) is allowed and will not affect validation:

module.exports.extra = 'some extra value'
module.exports.handler = async (input, output) => {
  output.setResult({ message: 'Hello' })
  return output.buildOutput()
}

JavaScript Syntax

Valid JavaScript

Your code must be syntactically valid JavaScript. Common syntax errors include:

Missing closing braces
Unmatched parentheses
Invalid syntax

// ❌ Example of Syntax Error:
module.exports.handler = async (input, output) => {
  output.setResult({ message: "Hello" })
  return output.buildOutput(;  // Error: Unmatched parenthesis
};

Common Validation Error Messages

You may encounter the following validation errors:

"Module 'unknown/chains' is not approved"
"User code must export exactly one handler function"
"Invalid dynamic require detected"
"Failed to validate user code: ..."
"The 'handler' property must be assigned to a function"
"Multiple handler definitions found"
"The 'handler' function must accept exactly two parameters: 'input' and 'output'"
"The 'handler' function must use output.setResult"
"The 'handler' function must call output.buildOutput()"

Examples

Valid Stratus Function with External Module

const axios = require('axios')

module.exports.handler = async (input, output) => {
  const response = await axios.get('https://example.com')
  output.setResult({ data: response.data })
  return output.buildOutput()
}

Valid Function Without External Modules

module.exports.handler = async (input, output) => {
  output.setResult({ message: 'Hello World!' })
  return output.buildOutput()
}

Common Mistakes

Multiple Handler Exports

// ❌ Incorrect: Multiple handler definitions
module.exports.handler = async (input, output) => { ... };
module.exports.handler = async (input, output) => { ... };

Missing Output Calls

// ❌ Incorrect: Missing output.setResult
module.exports.handler = async (input, output) => {
  return output.buildOutput();
};

Dynamic Require Usage

// ❌ Incorrect: Dynamic require
const mod = 'axios';
const axios = require(mod);

Summary

To ensure your Stratus function passes syntax validation:

Export one handler function using the correct module export syntax
Ensure the handler is asynchronous and accepts exactly two parameters: input and output
Call both output.setResult and output.buildOutput() within your handler
Import only approved modules using string literals (no dynamic requires)
Write valid JavaScript with correct syntax

​Overview

​Module Export & Handler Function

​Single Handler Export

​Proper Export Format

​Handler Function Parameters & Behavior

​Parameter Requirements

​Using output.setResult

​Calling output.buildOutput()

​Module Import Requirements

​Allowed Modules

​Disallowed Modules

​Extra Exports

​JavaScript Syntax

​Valid JavaScript

​Common Validation Error Messages

​Examples

​Valid Stratus Function with External Module

​Valid Function Without External Modules

​Common Mistakes

​Summary

Overview

Module Export & Handler Function

Single Handler Export

Proper Export Format

Handler Function Parameters & Behavior

Parameter Requirements

Using output.setResult

Calling output.buildOutput()

Module Import Requirements

Allowed Modules

Disallowed Modules

Extra Exports

JavaScript Syntax

Valid JavaScript

Common Validation Error Messages

Examples

Valid Stratus Function with External Module

Valid Function Without External Modules

Common Mistakes

Summary