performance critical change

[jerch]

@Tyriar You recently added the new Uint8Array(...) here:

xterm.js/addons/addon-image/src/IIPHandler.ts

Line 108 in b2133d9

const blob = new Blob([new Uint8Array(this._dec.data8)], { type: this._metrics.mime });

Imho that is a subpar change, as the Blob ctor already synchronously copies the data, with the array ctor it becomes a copy of a copy?

[Tyriar]

This was to make the new TS types happy, would [this._dec.data8.buffer] work instead?

[Tyriar]

Also this doesn't copy the array does it, it's just a lightweight view on top of the same ArrayBuffer?

[jerch]

this._dec.data8 is a .subarray() into the wasm memory, so just a byte view. What should work:

[this._dec.data8 as Uint8Array<ArrayBuffer>]

This is basically the same as before, just one copy by the blob ctor. [this._dec.data8.buffer] does not work, as it would copy the full wasm memory over.

Another approach would be:

const data = this._dec.data8;
new Uint8Array(data.buffer, data.byteOffset, data.length);

but that calls the Uint8Array ctor for no good reason at all, because data8 is already a Uint8Array.

[Tyriar]

#5661

[jerch]

Gonna upgrade the xterm-wasm-parts package, then the issue with the types should be gone.

Btw I just upgraded the inwasm wasm compile tool, it now supports ESM modules too. (Was quite involved to get this done haha).

[Tyriar]

I'd love to move to ESM in vscode and explore code splitting (#5610), seems like a pretty scary change though

[jerch]

To be honest it scared me too, but in the end it was a pretty straight forward change:

• adjust tsconfig to nodenext
• repair local imports to xxx.js

The biggest benefit I see with ESM is getting await/async on modules top level (we don't really need that in xterm.js though, as we carefully worked around it so far) and the better tree shaking for bundling. The resulting packages are much smaller.

What was annoying though in inwasm - the cli needs to separate ESM and CommonJS with different eval strategies.

Edit: And yes - the partial sub exports is a big win. We could just mark typical addon parts from core as exported and then import them in addons as needed.