> For the complete documentation index, see [llms.txt](https://docs.stacksync.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.stacksync.com/agentic-workflows/features/code-execution/javascript-code-execution.md).
# Javascript Code Execution
Run custom JavaScript scripts directly inside your workflow. Use it for fast data formatting, string manipulation, date operations, or lightweight logic between nodes.
### 1. Add the Module
Add the **JavaScript Code** module to your workflow as an action node.
### 2. Pass Data In Context
In the module configuration panel, add context variables under the **Context** section. Each entry takes a **Name** and a **Value** use the variable picker to map values from upstream nodes.
Each context entry becomes a key on `WORKFLOW_CONTEXT` inside your script:
```javascript
function main(WORKFLOW_CONTEXT) {
const amount = WORKFLOW_CONTEXT.amount;
const currency = WORKFLOW_CONTEXT.currency;
}
```
### 3. Write Your Script
Your script must define a `main` function. Stacksync automatically injects `WORKFLOW_CONTEXT` as the argument containing all your context values.
```javascript
function main(WORKFLOW_CONTEXT) {
const amount = WORKFLOW_CONTEXT.amount;
const currency = WORKFLOW_CONTEXT.currency;
return {
amount: amount,
currency: currency
};
}
```
### 4. Return Data
Whatever `main` returns becomes the node's output, available to downstream nodes via standard node referencing.
Reference in downstream nodes:
```
{{ your_module_id.amount }}
{{ your_module_id.currency }}
```
> **Debugging:** `console.log()` output is captured and surfaced under `metadata.stdout` in the execution logs. Use it for debugging, it does not pass data downstream.
### Available Libraries
| Library | Use case |
| --------------------------- | --------------------------- |
| `dayjs` | Date parsing and formatting |
| `moment` | Date manipulation |
| `live-plugin-manager` | Dynamic module loading |
| Node.js 23 standard library | All built-in modules |
> **Note:** You cannot install additional packages at runtime with `npm install`.
### Limits
| Limit | Value |
| ---------------- | -------------------- |
| Timeout | 6s |
| Memory | 8 GB |
| Filesystem | Read-only, no writes |
| Runtime packages | Pre-installed only |
> **Watch out:** Avoid using JavaScript for slow HTTP calls, heavy loops, or large dataset operations as the timeout is 6 seconds, use the Python Code module instead.
