@fuzdev/tsv_wasm

precise language tools for TypeScript/JS, CSS, and Svelte in Rust

Rust-based formatter + parser compiled to WASM — the full tool in one package, with a tsv CLI. A near-Prettier formatter that tracks Prettier + prettier-plugin-svelte closely (with documented divergences), plus a drop-in replacement parser for Svelte's parser + acorn + acorn-typescript.

Only need one half? The subset packages ship smaller WASM blobs: @fuzdev/tsv_format_wasm (format only) and @fuzdev/tsv_parse_wasm (parse only).

Source of truth, full docs, and conformance notes: github.com/fuzdev/tsv.

CLI

npx @fuzdev/tsv_wasm format src        # format .ts/.mts/.cts/.js/.mjs/.cjs/.svelte/.css in place, recursively
npx @fuzdev/tsv_wasm format --check .  # CI: exit 1 if anything would change
npx @fuzdev/tsv_wasm format --list .   # list the in-scope files, format nothing
npx @fuzdev/tsv_wasm parse file.svelte # JSON AST to stdout (--pretty to indent)

Installed (npm i -D @fuzdev/tsv_wasm), the bin is tsv. Directories recurse over .ts/.svelte/.css with gitignore-aware discovery. Inside a git repo it honors .gitignore, .formatignore, and .prettierignore (all hierarchical, like git), scoped to the repo so results are reproducible. Outside a repo it honors only .formatignore, falling back to skipping hidden directories and dist/build/target. node_modules and VCS directories are always skipped; an explicitly named file is always formatted.

format --list prints the discovered in-scope files without formatting — a read-only view of what format would touch. --content <source> / --stdin (with --parser svelte|typescript|css) format or parse strings to stdout. For TypeScript, --goal script|module (default module; for format, --content/--stdin only) selects the parse goal — at script, await is an ordinary identifier and import/export/import.meta are errors. parse --no-locations emits the span-only wire (no per-node loc; Svelte also no name_loc; no-op for CSS). Exit codes — format: 0 clean, 1 would-change (--check), 2 errors; parse: 0 ok, 1 error.

This CLI runs the single-threaded WASM build — plenty fast for most trees. A future native tsv binary will be the high-performance path.

Library usage

In Node.js, Bun, and Deno, WASM is initialized synchronously at import time — zero config. In browsers and bundlers, call await init() once first (Vite, Webpack, and Rollup resolve the WASM asset automatically; init_sync({ module }) is also exported for Workers and custom loading).

import {format_svelte, parse_svelte} from '@fuzdev/tsv_wasm';
import type {Root} from '@fuzdev/tsv_wasm';

const formatted = format_svelte('<script>\nconst   x=1\n</script>');
const root: Root = parse_svelte('<script>const x = 1;</script>');

Three formatters (format_svelte, format_typescript, format_css) take a source string and return the formatted string. Three parsers (parse_svelte, parse_typescript, parse_css) return a Svelte-compatible JSON AST; the parse_*_json variants return the AST as a compact JSON string instead (faster when writing to disk or the wire). For TypeScript and Svelte, parse_{typescript,svelte}_no_locations (and _json_no_locations) emit a span-only wire — start/end offsets, no per-node loc (Svelte also no name_loc) — ~46% smaller and faster to materialize, with line/column derivable from offsets + source. All throw on a parse error.

To turn a span-only wire back into a loc-bearing one, reconstruct_locations(ast, source) adds loc to every node (mutating in place; structuredClone first to keep the input) — exact for TypeScript (each node's loc value equals acorn's; the key is appended last, so an object consumer matches but a re-serialized tree won't byte-match the wire's key order), approximate for Svelte (no name_loc, and it skips Svelte's <script>/destructure position quirks), a no-op for CSS. For sparse lookups, create_locator(source, opts?) reuses one line table across loc_of(node) / reconstruct(ast) calls (pass {language: 'svelte'} for .svelte); a bare loc_of(node, source) is also exported.

AST types are bundled in tsv_ast.d.ts and re-exported from the package — import type any node directly.

tsv is non-configurable: formatter settings are fixed at Prettier's defaults except printWidth: 100, useTabs: true, singleQuote: true, and trailingComma: 'none' — no options, like gofmt and Black.

Status

v0.1 — pre-release. API may change.

License

MIT