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Configuration ​

json-as is configured at build time through environment variables read by the transform — there's no runtime config object. Set them on the asc invocation (or your build script's env).

JSON_MODE ​

Selects the scanning backend. All three produce identical results; they differ in speed and code size.

bash
JSON_MODE=SWAR  asc … --transform json-as              # default
JSON_MODE=SIMD  asc … --transform json-as --enable simd
JSON_MODE=NAIVE asc … --transform json-as
  • SWAR (default) — word-at-a-time. No extra flags.
  • SIMD — 128-bit vector scanning; requires --enable simd.
  • NAIVE — byte-at-a-time; smallest, slowest.

JSON_USE_FAST_PATH ​

The transform generates an unrolled, key-template fast path for deserializing each struct, with a tolerant slow path as fallback. On by default; set to 0 to emit only the slow path (smaller code, slower parse).

bash
JSON_USE_FAST_PATH=0 asc … --transform json-as

JSON_CACHE ​

Enables an interned-string cache that speeds up string-heavy serialization by reusing repeated strings. Off by default. Pass a size to enable it — raw bytes, or units like 512kb, 1mb, 2MB:

bash
JSON_CACHE=1mb   asc … --transform json-as   # enable, 1 MB cache
JSON_CACHE=false asc … --transform json-as   # off (default)

JSON_STRICT ​

Tightens parsing toward strict RFC 8259 — the generated object scanner rejects malformed key positions (unquoted/numeric keys, missing separators) instead of accepting them. The default build is lenient.

bash
JSON_STRICT=true asc … --transform json-as

JSON_WRITE ​

Writes the transformed source (your file with the generated __SERIALIZE / __DESERIALIZE methods spliced in) to <path>.tmp.ts, for inspecting generated code.

bash
JSON_WRITE=assembly/index.ts asc assembly/index.ts --transform json-as

In asconfig.json ​

The transform itself is registered in asconfig.json; the variables above are environment, so set them in the command or your build tooling:

json
{
  "options": {
    "transform": ["json-as"]
  }
}
bash
JSON_MODE=SIMD asc assembly/index.ts --config asconfig.json --enable simd