Keyed each blocks break with component named Map

[s3ththompson]

Keyed each blocks break with a component named Map, throwing the error 'target' is a required option. (Note, this happens whether Map is the component inside the block or the component with the each block in its template.)

It took a while to track this down... is Map a reserved component name? If so, is there any chance the error message could be improved?

https://svelte.dev/repl?version=3.1.0&gist=0f12697412a5adacf701e3f5b14f9a8a

[EmilTholin]

Svelte uses a Map to keep track of elements in the keyed each block, and the global Map constructor is shadowed by the component and throws an error.

function create_fragment(ctx) {
  var button, t_1, each_blocks = [], each_1_lookup = new Map(), each_1_anchor, current, dispose;
  // ...
}

[Conduitry]

svelte/src/compile/render-dom/wrappers/EachBlock.ts

Line 297 in c988457

block.add_variable(lookup, `new Map()`);

What would fix this in this case is using new window.Map here, but in general I'm not really sure how we want to handle deconflicting these sorts of things. There could be a bunch of common globals that generated code is currently assuming it's able to access.

[tomblachut]

@Conduitry Hmmm $ prefix is reserved already. What about aliasing used globals with it?

[Rich-Harris]

can confirm this is fixed in 3.6.0