o:type

Syntax

<script type=application/json o:=app.webmanifest o:type=application/manifest+json>{"name":"Demo"}</script>
<script type=text/plain o:=notes.txt o:type="text/plain;charset=utf-8">Café notes</script>
<script type=text/markdown worker:fs=notes.md o:type=text/markdown>…</script>

Value

type/subtype

A MIME type, optionally with parameters such as ;charset=utf-8. Quote a value that contains =, as ;charset=utf-8 does. The value is used as written and is not validated: o:type="" produces an empty content type on RTEdge.net and ;charset=utf-8 in the playground.

Default

Without the attribute, the type comes from the extension table, then from the MIME type of a data: URL, then from the binary or text default.

Description

The extension is the text after the last . of the file name, lowercased, so x.JS is text/javascript. Both environments use the same extension table; RTEdge.net adds one entry, wasm.

Exported files

Worker assets

For a worker:fs asset, env.FS[key].type is o:type, else the type for the extension of the key (the whole key when it has no dot, so worker:fs=json gets application/json), else the MIME type of a data: URL, else application/octet-stream for binary data. It is undefined for a text key with an unknown extension. No charset is added.

Usage notes

Charset

For non-ASCII text that visitors open directly, such as .txt, .md and .csv files, give the charset yourself: o:type="text/plain;charset=utf-8". Quote the value, because an unquoted value that contains = is an HTML parse error, even though browsers accept it. A page exported from a <template> should start with <meta charset=utf-8>, since RTEdge.net serves table types without a charset.

Types missing from the table

The table has no entry for webmanifest, map, yaml, yml, toml, vtt, jsx, tsx or glb, and none for wasm in the playground. Those names fall back to the default text type, so set o:type on them. ts maps to video/mp2t, so a TypeScript file needs o:type as well.

Elements that share a name

When elements share a file name, the file keeps the type of the first element. The o:type of the later ones is silently ignored.

o:type and h:content-type

The playground ignores h:content-type, and RTEdge.net lets it win. Set o:type when you want the same result in both. For worker:fs assets, set o:type rather than h:content-type.

A wrong type blocks scripts and styles

Responses on RTEdge.net carry x-content-type-options: nosniff. A script or stylesheet served with the wrong type therefore does not run or apply, so check the type of every export you load that way.

On deploy

Deploy strips o:type from the served HTML and from export bodies. The deployed source keeps it.

Pre-compressed WebAssembly

Experimental On RTEdge.net, a platform rule gives a path that ends in .wasm.br the headers Content-Encoding: br and Content-Type: application/wasm. It is meant for pre-compressed exports such as <img hidden o:=app.wasm.br src="data:;base64,…">. The playground has no such rule and serves application/octet-stream;charset=utf-8. The encoding a browser finally receives can differ from the header, so test a real export before you rely on it.

Extension table

Both environments map these extensions, case-insensitively, to these types. Table types are served without a charset on RTEdge.net, and with ;charset=utf-8 appended in the playground.

RTEdge.net refuses requests for some names whatever their type; see Reserved paths.

Examples

Text with a charset

<script type=text/plain o:=notes.txt o:type="text/plain;charset=utf-8">Café, naïve, 日本語</script>
<iframe src=notes.txt></iframe>

A web app manifest

<script type=application/json o:=app.webmanifest o:type=application/manifest+json>{"name":"Demo"}</script>
<output id=kind></output>
<script type=module>
  kind.value = (await fetch('app.webmanifest')).headers.get('content-type')
</script>

The extension webmanifest has no table entry, so o:type sets the type. The output shows application/manifest+json;charset=utf-8; on RTEdge.net the header is application/manifest+json.

Specifications

Not part of any specification. o:type is an RTCode.io and RTEdge.net feature.

It builds on these standards:

Availability

See also

• Global attributes
• Exporting files
• o:
• h:*
• worker:fs
• Response headers
• Importing modules and WebAssembly