How to get a specific item from the collection

I want to know how I can get a specific item's view from the collection using index or some other way. @farfromrefug told me about getViewForItemAtIndex in #17 but haven't been able to make it work. I need to do some work on each item of the list when the user presses a button (not part of collection). Here's my code:

const collection = page.getViewById('collection');

for (var i = 0; i < listItems.length; i++) {
  const listItem = collection.getViewForItemAtIndex(i);
  console.log(listItem); // undefined
}

Since there's no documentation on it, I'm just shooting in the dark here.

Start with the getViewForItemAtIndex entry point and the related discussion in issue #17. Clarify how item views are obtained from a collection, including why the call may return undefined, and document a supported example for work triggered by an external button.