Worked on the paypal/paypal-js repository to enhance code reliability by enforcing immutability within the ProcessOptions path. Addressed a bug where input arguments were being mutated by refactoring the code to replace delete statements with the spread operator, ensuring that original data remained unchanged during processing. Added comprehensive unit tests to verify that immutability was maintained and to prevent future regressions. Documented the update with a changeset to inform downstream consumers of the change. This work utilized JavaScript and TypeScript, with a focus on refactoring and testing practices to reduce runtime risk and improve maintainability in the codebase.