More information about text encoding when creating a Blob

[domleonard]

MDN URL

https://developer.mozilla.org/en-US/docs/Web/API/Blob/Blob

What specific section or headline is this issue about?

The note about strings under description of the array parameter

What information was incorrect, unhelpful, or incomplete?

The note for strings under the array parameter description states

Note that strings here are encoded as UTF-8, unlike the usual JavaScript UTF-16 strings.

This can be confusing and could be interpreted as meaning strings provided should be encoded in utf8 already and that standard JavaScript strings are not acceptable.

What did you expect to see?

Possibly a note worded more along the lines of

Note that string items in array are treated as Unicode text and serialized in Blob output using utf8 encoding. In particular, providing base64 or binary string values in array never converts them to binary data when a Blob is serialized.

Do you have any supporting links, references, or citations?

processing Blob Parts under Contructor parameters in the FIle API standard.

USVString in the Web IDL standard.

Do you have anything more you want to share?

No response

MDN metadata

Page report details

• Folder: en-us/web/api/blob/blob
• MDN URL: https://developer.mozilla.org/en-US/docs/Web/API/Blob/Blob
• GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/web/api/blob/blob/index.md
• Last commit: 15d7838
• Document last modified: 2023-02-19T04:00:18.000Z

[Josh-Cena]

It means strings have to be well-formed Unicode strings (USVString), without lone surrogates. It has nothing to do with UTF-8, as far as I'm concerned. Lone surrogates are replaced with U+FFFD (see toWellFormed()). We should change

Note that strings here are encoded as UTF-8, unlike the usual JavaScript UTF-16 strings.

to

Strings should be well-formed Unicode, and lone surrogates are sanitized using the same algorithm as {{jsxref("String.prototype.toWellFormed()")}}.