Update function does not work with __proto__ key
Author: olivercoadCreated Sep 7, 2026Updated Sep 7, 2026
What happened
A property-based test caught this edge case in my project and I traced the cause to Immutable Map update function.
How to reproduce
Map()
.set("__proto__", "set")
.update("__proto__", (u) => "updated")
.get("__proto__") // expected: "updated", actual: "set"
Source: immutable-js/immutable-js