Memory leak: scroll event listener not being removed

[abulrim]

Version

3.0.0

Steps to reproduce

• Enter route that has a component that uses in-viewport mixin on window
• Leave to route that doesn't have that component
• Check event listeners on window in the dev tools
• Notice scroll event still attached

Expected Behavior

Scroll events should be cleaned when element destroyed

Likely Culprit

The changes done to the _unbindListeners method in the in-viewport mixin in this PR (we return before reaching this._unbindScrollDirectionListener())

[abulrim]

Also removing the event listener in the current implementation won't work since the callback is a new function each time

[snewcomer]

@abulrim Great catch! The early return is my fault. Oversight by me. The second point - So we are passing in an anon callback; however, I'm also seeing this as I would only guess it is not a reference to the function object.

If you felt like submitting a PR to use Function.prototype.bind for both the scroll event listeners and the viewportListeners (or other solution you have), that would be great! Otherwise, I can push something up to fix these as well. Let me know! Again, thanks for bringing this up and documenting it so well.