Execute custom JS

The execute javascript interaction step allows you to execute arbitrary JavaScript or TypeScript code as part of your test flow. This is useful for performing custom logic, calculations, or interacting with APIs that are not directly accessible through other test steps.

'execute javascript' interaction option in a test step, 05/2025

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Isolation and limitations

• No direct access to Playwright or browser context: Your script cannot interact with page elements, cookies, or the DOM directly.
• Resource limits:
  • Runtime: Scripts are limited in execution time to prevent infinite loops and slow tests.
  • Memory: Scripts have a capped memory allocation.
  • Network: Outbound network requests may be restricted or rate-limited.

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Setting dynamic variables

You can create dynamic variables by printing a JSON object to stdout using console.log. These variables can be used in subsequent steps of your test.

For example, if your script creates a new document in your application and receives a document ID in the response, you can expose this ID as a dynamic variable:

// Example: Creating a document and exporting its ID as a dynamic variable
async function main() {
  const response = await fetch("https://api.example.com/documents", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ title: "My Document" }),
  });
  const data = await response.json();
  // Set the dynamic variable by logging a JSON object
  console.log(JSON.stringify({ documentId: data.id }));
}

main();

After this script runs, you can reference the dynamic variable in later steps using $$documentId.

Example: Exporting a dynamic variable from a JavaScript step

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Best practices

1. Keep scripts short and efficient to avoid hitting resource limits.
2. Validate outputs before logging dynamic variables to prevent errors in later steps.
3. Avoid sensitive operations since scripts run in an isolated environment with limited permissions.
4. Use dynamic variables to pass data between steps and make your tests more flexible.

By leveraging the execute javascript step, you can extend your tests with custom logic while maintaining security and reproducibility.