Julian Navarro

@juliannavarro

Backend engineer writing about language and design basics that still cause outages: copies, races, async gaps and code that fights its own abstractions.

Member since Nov 5, 2026

1 Stories

8 Views

0 Likes

0 Followers

Banner: shallow copy bug where nested objects stay shared between copies

Programming Languages Bug Report

A shallow copy let one request rewrite the defaults for every request after it

Julian Navarro · Nov 5, 2026 · 8 min read

We copied a config object with spread before customising it per tenant. The nested objects were still shared, so one tenant's override leaked into everyone else's defaults. How we found it, and the copy rules for JavaScript, Python and Go.