ListBar labels not working correctly

[gveres]

ListBars on current master show "undefined" around the actual labels. Otherwise the widget functions correctly, just the displayed label is corrupted.
Reproduce by running the widget-listbar.js test.
Am I missing something?
FYI, the version currently in npmjs works fine.
Thanks!

[cdaringe]

[{ key: "option1", callback: () => { }}, { key: "option2", callback: () => { }}] // not ok
{ option1: () => {}, option2: () => {} } // ok

hope it helps :)