event.type as a key to get the array of event handlers, which throws an exception when we instead receive an
Object.prototype property and treat it like an array: https://jsfiddle.net/9t4kqaqr/
Our standard fix is appending a space (cf. delegated selector match tracking and Sizzle
createCache), but we should also consider
Map for such purposes (ponyfilling as needed), especially if Data.js can be updated accordingly—one of @rwaldron‘s original goals when creating it.