andreypopp/autobind-decorator

Break sinon.spy(Component.prototype, 'method')

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#47 opened on May 7, 2017

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Description

When using '@autobind' on a component, then in tests sinon.spy(Component.prototype, 'someMethod') will yield an error:

TypeError: Attempted to wrap undefined property undefined as function
...

Sorry, currently I can't provide more detail, but I'm sure @autobind is the only variable between success/error in tests.

Contributor guide

Tech stack
javascript
Domain
frontend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
needs investigation
Prerequisites
basic understanding of JavaScript decoratorsfamiliarity with sinon spy
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
The issue occurs when using @autobind on a class component, then attempting to spy on a prototype method with sinon.spy. The error suggests that the property is undefined, likely because @autobind replaces the method with a getter or redefines properties. To reproduce, create a simple React component with @autobind on a method and test using sinon.spy(Component.prototype, 'method'). Investigate the autobind decorator source code (especially the core decorator logic) to understand how it binds methods and how that interferes with sinon's prototype spying. Consider if a workaround exists or if the decorator needs to be adjusted to preserve the property descriptor for spy compatibility.