Incorrect type returned by TextEncoder.encode

[aryzing]

🔎 Search Terms

TypedArray, Uint8Array, ArrayBufferLike, TextEncoder

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about TextEncoder

⏯ Playground Link

Playground link

💻 Code

const data = new TextEncoder().encode("hello")
//    ^? Uint8Array<ArrayBufferLike>
// The `ArrayBufferLike` may include `SharedArrayBuffer`, but `encode()` 
// only supports `ArrayBuffer`, so this breaks code expecting an `ArrayBuffer`.

function processData(d: ArrayBuffer) {
  // do stuff
}

processData(data.buffer) // This should work, but reported as type error

🙁 Actual behavior

Values returned by TextEncoder.encode are not assignable to ArrayBuffer.

🙂 Expected behavior

Values returned by TextEncoder.encode should be assignable to ArrayBuffer.

Additional information about the issue

https://stackoverflow.com/a/79300250/1494725

[KisaragiEffective]

I think this is expected behavior change introduced in 5.7 series.
Consider change ArrayBuffer to ArrayBufferLike which is an union of both ArrayBuffer and SharedArrayBuffer.

[jcalz]

This is definitely fallout from the TS5.7 change at #59417, but the question is whether it should be. Is TextEncoder.encode() known to produce a Uint8Array<ArrayBuffer>? I don't think it ever produces something else (there's encodeInto() that lets you bring your own buffer) but I'm no expert on these things. But if it is always producing a Uint8Array<ArrayBuffer> then it's probably best for the lib to reflect that. If it isn't, is that documented somewhere?

[aryzing]

Surfacing a link from the linked SO post,

https://encoding.spec.whatwg.org/#ref-for-dom-textencoder-encode%E2%91%A0

If result is finished, then convert output into a byte sequence and return a Uint8Array object wrapping an ArrayBuffer containing output.