Monkey Patching in JavaScript (2026): Safe Runtime Overrides

Monkey patching is changing or extending existing behavior at runtime, such as replacing a method on an object, module export, or prototype, without editing the source code.

Modifying prototypes is one common form of monkey patching in JavaScript. Monkey patching is broader: it also includes reassigning functions or methods on modules and plain objects.

Keep the patch scoped to the test, store the original implementation, and restore it in a teardown hook (for example, in an afterEach block or a finally clause).