> For the complete documentation index, see [llms.txt](https://docs.formsort.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.formsort.com/integrations/integration-reference/google-tag-manager/javascript-triggered-by-flow-events.md).

# JavaScript triggered by flow events

Run JavaScript via Google Tag Manager

Formsort integrates directly with a number of 3rd party tools. If the tool you need does not have a prebuilt integration, Google Tag Manager can be used to run JavaScript to extend Formsort's capabilities

{% hint style="info" %}
Running JavaScript via Google Tag Manager should only be done as a last resort. Formsort cannot provide support for this functionality or guarantee that it will not negatively impact your flows.
{% endhint %}

### Custom events

Formsort dispatches custom events via [custom event api](https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent/CustomEvent). These events can be listened to and used to trigger JavaScript via Google Tag Manager.

The following is a list of events with payload definitions:

* `FlowLoaded`

```typescript
{
	flowLabel: string;
	variantLabel: string;
	deploymentUuid: string;
	experimentId?: string;
	formsortEnv: string; // production, staging etc.
}
```

* `StepLoaded`

```typescript
{
	stepIndex: number;
	stepId: string | number; // loaded step id, falls back to step index if step id is not given
	// and variant details defined in FlowLoaded
}
```

* `StepCompleted`

```typescript
{
  stepIndex: number,
  stepId: string | number;
  msSpentOnStep: number; // time in milliseconds user spent on this step
  // and variant details defined in FlowLoaded
}
```

* `FlowFinalized`

```typescript
{
  stepIndex: string; // final step index
  stepId: string | number; // final step id falling back to index number
  redirectUrl?: string; // redirect url of final step (optional)
  // and variant details defined in FlowLoaded
}
```

### Example function

The following JavaScript for a mock analytics service can be triggered in Google Tag Manager based on a single step of a multi-step flow via the `StepLoaded` event.

```javascript
window.addEventListener('StepLoaded', (event) => {
	const payload = event.details;
	
	if (payload.stepId === 'watch_this_step') {
		const thirdPartyScript = document.createElement('script');
		thidrPartyScript.src = '...';
		document.head.appendChild(thidrPartyScript);
		
		fetch('my-api-url.com/record-start-event', {
			method: 'POST',
			body: JSON.stringify({ flowLabel: payload.flowLabel, timeStamp: +Date.now() }),
			headers: {
				'content-type': 'application/json',
			},
		})
	}
});

window.addEventListener('StepCompleted', (event) => {
	const payload = event.details;
	
	if (payload.stepId === 'watch_this_step') {
		window.thirdPartyService.stopRecording();
		
		fetch('my-api-url.com/record-end-event', {
			method: 'POST',
			body: JSON.stringify({ flowLabel: payload.flowLabel, timeStamp: +Date.now() }),
			headers: {
				'content-type': 'application/json',
			},
		})
	}
});
```


---

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