The JavaScript step is the tool to use when performing a desired action is not possible with the trace recorder.
Some use case examples are mentioned in the Javascript Examples page.

This tool consists of a code editor section where the user can input code that will be executed in the browser,

a search field with pre-recorded JS templates,

and project-based saved JS templates (a feature that enables users to save and reuse their code in the project they work on by adding a template name and saving the template).

There is an option to obtain AI-generated code with simple word-based search instructions.
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The code used in the code area can be validated using the "Run code in the virtual browser" button.