How does this prevent an instance of any old class named "File" or "Blob" being detected as a File or Blob?

Maybe ensure that methods are present on obj that we will call later on?

this sounds a good idea

Because the const { Blob } = ... line was removed, this is now the global Blob so TS will be unhappy if someone explicitly passes @web-std/file objects in your code.

Might just need to remove the @returns annotation so tsc will derive a boolean return type.

return the @returns causes typescript to also not be happy, I added globalThis to the type

File extends Blob so under what conditions would we need to fall back here?

instanceOf is tricky.
File https://github.com/web-std/file/blob/default/src/lib.js#L6 extends from Blob as you mention, and Blob is https://github.com/web-std/io/blob/main/blob/src/lib.js (so the same as here).

But, somehow this will not work with instanceOf Blob, and works with @web-std/blob. So, if you create a Blob and a @web-std/blob, their instanceOf are not compatible...

This sounds like @web-std/blob needs to return the native implementation if it's available?

Also of note here is that node 16 has a Blob implementation.

This sounds like @web-std/blob needs to return the native implementation if it's available?

It does: https://github.com/web-std/io/blob/main/blob/src/lib.js

but instanceOf returns false 🤷🏼‍♂️

I changed it now to Blob to be:

const { Blob } = require('@web-std/blob')

instead of

const { Blob } = globalThis

It works this way, but then other tests fail (which probably use the native Blob 🤷🏼‍♂️

reverting this, as this is even more problematic

So, when creating a https://github.com/web-std/io/tree/main/file in the browser, it will not be an instance of Blob, but it will be of https://github.com/web-std/io/tree/main/blob. This is really weird, given that ws Blob is really globalThis.Blob.

This codepen shows that a browser File should be instance of both Blob and ws Blob.

My only assumption for this to not be the case in the tests here, is that somehow playwright has a different globalThis scope in the test that makes them being different... @hugomrdias is this reasonable? do you have any clues?

web-std/io#10 this fixed the issue

Now @web-std/file uses the Node.js version with Eletron renderer 😡