Deep copy data

I need a reliable deep copy of this userSettings object before I modify it. Copy every nested object and array so mutating the copy won’t touch the original. Keep functions, Dates and RegExp intact and preserve prototype links where possible. I will then run transformations for display. Make the copy here and confirm its top-level keys match the original.

Before I wire this into the form code, make the deep copy easier to validate: show the total number of nested keys, surface any properties that are functions, Dates or RegExp at the top, and flag fields that look like DOM nodes or circular references that would break serialization.

I just copied sessionState, applied changes in the UI, and found the original mutated. sessionState is used by other modules and I can’t tell where a reference leaked. I’m afraid my copy logic missed nested arrays or prototype-linked objects. I don’t know whether the leak came from a function property or a Date. What likely went wrong and what exact check-and-fix should I run now to prevent mutation escape?

Across projects I keep introducing bugs from shallow copies: form edits overwrite shared state and tests flake. I spend time tracking down which module mutated the shared object. Which habit should I change in my workflow to stop this recurring pain, and what small checklist or helper function would save the most time on future copies?