> ## Documentation Index
> Fetch the complete documentation index at: https://docs.snagsolutions.io/llms.txt
> Use this file to discover all available pages before exploring further.
# Functions
> Write and deploy serverless JavaScript functions on Snag Stratus. Schedule via cron, trigger via webhooks, or chain to onchain subscriptions for custom reward logic.
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## Overview
Stratus functions enable developers to write and execute JavaScript functions in a serverless environment. These functions:
* Scale horizontally
* Run in isolated VMs
* Have web access for external integrations
* Support complex logic combinations
Functions can interact with external services, allowing you to integrate with your own database, subgraphs, and other services.
## Invocation Types
Execute functions on a cron schedule with minimum 1-minute resolution
Invoke functions via HTTP POST requests using API keys
Trigger functions automatically when subscribed events occur
### Schedule Invocation
While there's no maximum schedule limit, the minimum resolution is 1 minute. Schedules with smaller intervals will fail.
### Webhook Invocation
To invoke functions via webhook:
1. Create a Stratus-scoped API key in the admin panel
2. Use the unique webhook URL assigned to your function
```bash Webhook Example theme={null}
curl --request POST \
--url https://admin.snagsolutions.io/api/stratus/functions//invoke \
--header 'Content-Type: application/json' \
--header 'X-API-KEY: ' \
--data '{
"organizationId": "org-1234",
"websiteId": "site-5678",
"input": {
"foo": 123,
"bar": "example value"
}
}'
```
### Subscription Invocation
Functions linked to subscriptions execute automatically when subscription events fire. Unlike webhooks, subscription-based invocations receive a single payload per event.
## Writing Functions
### Basic Structure
All Stratus functions must follow these rules:
Only one handler function can be exported per file
Handlers must be asynchronous
Functions must accept `input` and `output` parameters
```javascript Basic Template theme={null}
module.exports.handler = async (input, output) => {
// Your function logic here
};
```
### The Output Class
The `output` parameter provides methods for managing function results and actions:
Sets the function result data (called once before buildOutput)
```typescript theme={null}
setResult(resultObject: Record): void
```
Logs a failure and stops future executions
```typescript theme={null}
setError(error: string): void
```
Adds a transaction to the execution queue (requires relayer connection)
```typescript theme={null}
addTransaction(tx: Pick): void
```
Finalizes and returns the function output (required)
```typescript theme={null}
buildOutput(): Record
```
## Executing Transactions
To execute transactions, your function must be connected to a relayer in your account.
### Transaction Rules
* Maximum 500 transactions per function run
* Transactions execute in the order they're added
* All transactions use the connected relayer
## Approved Modules
Only pre-approved npm modules can be used in Stratus functions. Contact Snag Solutions if you need additional modules.
Currently approved modules:
* [`axios`](https://axios-http.com/)
* [`lodash`](https://lodash.com/docs)
* [`viem`](https://viem.sh/)
* `ioRedis`
* `upstash/redis`
## Example Function
```javascript theme={null}
const axios = require('axios');
module.exports.handler = async (input, output) => {
try {
// Make an external API call
const response = await axios.get('https://api.example.com/data');
// Set the result
output.setResult({
data: response.data,
timestamp: Date.now()
});
// Add a transaction if needed
output.addTransaction({
to: '0x123...',
data: '0x456...',
value: '0'
});
// Return the built output
return output.buildOutput();
} catch (error) {
output.setError(`Function failed: ${error.message}`);
return output.buildOutput();
}
};
```
Contact Snag Solutions if you need access to additional npm modules for your Stratus functions.
## Related pages
Reference guide for exports, parameters, and module imports.
Pre-built templates for airdrops, token gating, and rewards.
Trigger functions automatically from onchain events.
Configure the loyalty program that functions can interact with.