Implement localStorage

[dsseng]

Implement localStorage and sessionStorage following the MDN spec, sessionStorage

[kitsonk]

In #1181 we discussed that these could be external modules added to the Deno registry and there wasn't a need for them to be part of the core of Deno.

[ry]

I changed my mind. I think local storage would be really useful for serverless situations - imagine you have a server and you want to store a simple chat log or counter - with localStorage we can circumvent using a database nor expose the disk. Let's do it!

[akmittal]

Wont it be better to support sqlite by default, Something like android does. localStorage would be too limited.

[kitsonk]

localStorage is a published API that people expect to be there. IndexDB is another. Supporting sqlite is actually tangental to supporting browser standard APIs.

[ry]

https://developer.mozilla.org/en-US/docs/Web/API/Cache
Would be cool to have this as a lower-level storage that localStorage is implemented on top of.

Also- should be noted that the reason we want this in core is that Cache/localStorage should be accessible even when --allow-read and --allow-write are off.

[zekth]

What's the policy for the cache? Is it persistent if the runtime turns off or not?

[ry]

@zekth it's persistent

[zekth]

So if we use something like indexDB it will be shared by all scripts using the Deno runtime? If so, have to ensure there is no overlapping. Also do we add any maximum cache size or a permission for the max size?

[kitsonk]

I believe they are part of the spec or defacto standards in browser implementations.

[zekth]

Reference: https://chromiumcodereview.appspot.com/21680002

[axetroy]

In Chrome, LocalStorage uses leveldb

Maybe implement leveldb before implementing LocalStorage

Although the specification does not specify what db to used