Prevent auto-instantiation of components with oncreate

[Rich-Harris]

Because components are currently recompiled and reinstantiated on each keystroke, work that happens in an oncreate handler happens over and over again, which can be a little annoying in some cases (e.g. if you're doing a fetch, and it keeps making requests for non-existent resources because you're in the middle of typing the URL).

One way we could prevent that is by waiting for user input before instantiating components — e.g. expecting a Cmd-Enter or a button click.

The same is true for e.g. media elements.

Easiest thing to do is probably to have an option that lets you choose between as-you-type and on-command instantiation. One step beyond that would be to automatically choose between the two based on whether there's an oncreate or a media element (or any other similar conditions?). That would require that we have access to the component's AST, which would presumably mean updating svelte.compile to return a {code, map, ast} object instead of just code and map.

[Rich-Harris]

Oh, and import declarations

[Ryuno-Ki]

Have you considered throttling or debouncing it?

[Ryuno-Ki]

Interesting to learn, that it can be turned into an attack in some implementations: https://blog.0day.rocks/practical-waterholing-through-dns-typosquatting-e252e6a2f99e

[Rich-Harris]

This has been implemented crudely for some time, and less crudely now that we have stats sveltejs/svelte#1299