> For the complete documentation index, see [llms.txt](https://docs.sealights.io/knowledgebase/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.sealights.io/knowledgebase/setup-and-configuration/sealights-agents-and-plugins/node.js-agent/capturing-runtime-coverage.md).

# Capturing Runtime Coverage

After [Scanning Your Application](/knowledgebase/setup-and-configuration/sealights-agents-and-plugins/node.js-agent/scanning-your-application.md), make the app report coverage while tests run.

SeaLights supports two runtime coverage modes. Pick the one that matches your application.

| Mode                                                                                                                                                                                 | Command               | Use for                                          | What it does                                        |
| ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | --------------------- | ------------------------------------------------ | --------------------------------------------------- |
| [Frontend Instrumentation (static)](/knowledgebase/setup-and-configuration/sealights-agents-and-plugins/node.js-agent/capturing-runtime-coverage/frontend-instrumentation-static.md) | `instrument`          | Angular, React, Vue, and bundled JavaScript apps | Rewrites the built files before deployment.         |
| [Backend Instrumentation (dynamic)](/knowledgebase/setup-and-configuration/sealights-agents-and-plugins/node.js-agent/capturing-runtime-coverage/backend-instrumentation-dynamic.md) | `run` or `preload.js` | Node.js services, APIs, and workers              | Attaches at startup and instruments code in memory. |

{% hint style="info" %}
The deployment model is different for each mode:

* **Static frontend:** deploy the instrumented output, usually `sl_dist`, to a test environment only.
* **Dynamic backend:** deploy the original code and start it through the agent.
  {% endhint %}

For serverless Node.js backends on AWS Lambda, use [AWS Lambda Support](/knowledgebase/setup-and-configuration/sealights-agents-and-plugins/node.js-agent/capturing-runtime-coverage/aws-lambda-support.md).

### Choose the right page

* **Frontend app** — [Frontend Instrumentation (static)](/knowledgebase/setup-and-configuration/sealights-agents-and-plugins/node.js-agent/capturing-runtime-coverage/frontend-instrumentation-static.md)
* **Backend service** — [Backend Instrumentation (dynamic)](/knowledgebase/setup-and-configuration/sealights-agents-and-plugins/node.js-agent/capturing-runtime-coverage/backend-instrumentation-dynamic.md)
* **AWS Lambda** — [AWS Lambda Support](/knowledgebase/setup-and-configuration/sealights-agents-and-plugins/node.js-agent/capturing-runtime-coverage/aws-lambda-support.md)


---

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