arrowjs reactivity

[haoyun]

drag-and-drop/docs/examples/introduction/introduction.ts

Line 10 in d23853b

${state.items.map((item) => html`<li>${item}</li>`.key(item))}

should all examples like this be replaced by a "dynamic expression" according to https://www.arrow-js.com/docs/#templates.

Otherwise, the html is "static".

[tonekk]

Can confirm, none of the "vanilla" JS examples work.
Apart from the fact that they're actually in typescript, they lack reactivity, as @haoyun said.

All of the map calls need to be wrapped in arrow functions.