Resize events for DOM elements!

( resize the window or )

What is this? The <map-element> above is a custom element. Its definition ? inherits from a class mixin named ResizeObservableElement ?. It attaches a ResizeObserver to the element in order to know when its dimensions change. The element allows customers of the map element to hook in to this signal by attaching an onresize handler to the map element. Chrome 64+ supports ResizeObserver.