A tiny, predictable parser for Markdown fenced code block info strings. It extracts language, attributes, and line highlights with zero dependencies.

• Language: ts
• Attributes: key=value and bare flags; quoted strings with escaping (\n, \t, \", \', \\)
• Line highlights: {1,3-5} and attribute aliases highlight="1,3-5", lines="1,3-5", hl="1,3-5"
• Extras: extractBlocks, parseBlocks, normalize, parseLineSpec

Note: GitHub (GFM) ignores everything after the language in the info string. {...} and attrs are meant for site generators (VitePress, Nuxt Content, Astro, rehype-pretty-code, etc.), not for github.com.

sample.md:

# axios

```js
// GET request
const response = await fetch('https://api.example.com/data');
```

Script:

import { readFile } from 'node:fs/promises'
import { parseBlocks, normalize } from 'md-fence' // adjust import path if local

const md = await readFile('sample.md', 'utf8')
const blocks = parseBlocks(md)
const results = blocks.map(b => ({ info: b.info, meta: normalize(b.meta), code: b.code }))
console.log(JSON.stringify(results, null, 2))

Output:

[
  {
    "info": "js",
    "meta": { "lang": "js", "highlight": [], "attrs": {} },
    "code": "// GET request\nconst response = await fetch('https://api.example.com/data');\n"
  }
]

Add metadata:

```ts {1,3-5} title="App.tsx" line-numbers
const a = 1
function foo() {}
foo()
bar()
baz()
```

Normalized meta:

{ "lang": "ts", "title": "App.tsx", "lineNumbers": true, "highlight": [1,3,4,5], "attrs": {} }

• Language: first bare token (e.g. js, ts, bash)
• Attributes:
  • key=value (numbers and true/false are coerced)
  • key (boolean flag → true)
  • Strings: "..." or '...' with escapes: \n, \t, \", \', \\
• Line highlights:
  • Curly: {1,3-5}
  • Or attributes: highlight="1,3-5", lines="1,3-5", hl="1,3-5"

• parseInfo(info: string, opts?)
  • Returns { lang?: string; attrs: Record<string, string|number|boolean>; highlight: number[] }
  • Options: { lowerCaseKeys?: boolean } (default true), { treatFirstBareAsLang?: boolean } (default true)
• extractBlocks(md: string)
  • Returns Array<{ info: string; code: string }>
  • Supports backtick and tilde fences with matching lengths and up to 3 spaces indent
• parseBlocks(md: string, opts?)
  • Returns Array<{ info: string; code: string; meta: ReturnType<typeof parseInfo> }>
• normalize(meta, options?)
  • Maps known keys and merges highlight aliases
  • Default key map:
    • title → meta.title
    • filename|file|name → meta.filename
    • line-numbers|linenumbers|linenos → meta.lineNumbers
    • pinned → meta.pinned
    • collapsed → meta.collapsed
    • highlight|lines|hl → merged into meta.highlight
  • Returns:
    • { lang?, title?, filename?, lineNumbers?, pinned?, collapsed?, highlight: number[], attrs: Record<string, string|number|boolean> }
• parseLineSpec(value)
  • "1,3-5" → [1,3,4,5]