@willbooster/tree-sitter-javascript

JavaScript and JSX grammar for tree-sitter, forked from tree-sitter/tree-sitter-javascript. We are grateful to its authors and contributors. This is not an official release of that project.

This fork fixes parsing bugs and raises conformance with ECMAScript (ECMA-262) and JSX.

Support Scope

This fork maintains only full parsing: valid input yields a correct tree, and invalid input yields ERROR or MISSING nodes without crashing, hanging, or taking more than linear time. Incremental parsing works as in upstream tree-sitter but is not tested here, and no queries (highlights, locals, injections, tags) are shipped. Node types, field names, and the trees that error recovery produces may change; such changes are released as new major versions.

Usage

The npm package ships two languages for @willbooster/web-tree-sitter, which runs in Node.js, Bun, browsers, and Cloudflare Workers. The parser carries the ABI number of WillBooster/tree-sitter (0x5742000b), so it requires that runtime ABI; the upstream runtime rejects it. This package is tested with runtime 15.5.4, and its optional peer dependency covers major 15. In Node.js and Bun, load it from the package. Choose tree-sitter-javascript.wasm for the Module goal, or tree-sitter-javascript_script.wasm for the Script goal. The source goal comes from the host or file type; .mjs uses Module and .cjs uses Script, while .js depends on the host. For example, await\nvalue is one await expression in a Module and two identifier statements in a Script. Both languages preserve the same node schema. As with other tree-sitter grammars, parsing does not enforce every ECMAScript early error. For the native CLI, select Script with tree-sitter parse --grammar-path grammars/script.

import { fileURLToPath } from 'node:url';

import { Language, Parser } from '@willbooster/web-tree-sitter';

await Parser.init();
const parser = new Parser();
const wasmPath = fileURLToPath(import.meta.resolve('@willbooster/tree-sitter-javascript/tree-sitter-javascript.wasm'));
parser.setLanguage(await Language.load(wasmPath));
const tree = parser.parse('const App = () => <p>Hello</p>;\n');

In browsers, let your bundler serve the runtime and the selected language .wasm files, then pass their URLs. For the Script goal, replace the language import below with @willbooster/tree-sitter-javascript/tree-sitter-javascript_script.wasm?url:

import javascriptUrl from '@willbooster/tree-sitter-javascript/tree-sitter-javascript.wasm?url';
import { Language, Parser } from '@willbooster/web-tree-sitter';
import runtimeUrl from '@willbooster/web-tree-sitter/web-tree-sitter.wasm?url'; // Vite

await Parser.init({ locateFile: () => runtimeUrl });
const parser = new Parser();
parser.setLanguage(await Language.load(javascriptUrl));

In Cloudflare Workers, which do not allow compiling Wasm at run time, import the runtime and the selected language .wasm files as modules, with or without Node.js compatibility. For the Script goal, replace the language import below with @willbooster/tree-sitter-javascript/tree-sitter-javascript_script.wasm:

import javascript from '@willbooster/tree-sitter-javascript/tree-sitter-javascript.wasm';
import { Language, Parser } from '@willbooster/web-tree-sitter';
import runtime from '@willbooster/web-tree-sitter/web-tree-sitter.wasm';

await Parser.init({ wasmModule: runtime });
const parser = new Parser();
parser.setLanguage(await Language.load(javascript));

The package also ships the node types in src/node-types.json, tree-sitter.json, and grammar.js for grammars that extend this one (e.g. require('@willbooster/tree-sitter-javascript/grammar')). Its JSDoc describes the array/formal and object-rest extension hooks. The crate ships tree-sitter.json too.

In Rust, depend on the crate and the willbooster-tree-sitter runtime with the matching ABI. The tested version is 15.5.4:

cargo add [email protected] --rename tree-sitter
cargo add willbooster-tree-sitter-javascript --rename tree-sitter-javascript

let mut parser = tree_sitter::Parser::new();
parser.set_language(&tree_sitter_javascript::LANGUAGE.into())?;
// Use LANGUAGE_SCRIPT for the Script goal.

Development

mise install
bun install --frozen-lockfile
bun run build/ci
bun run test
script/parse-examples
cargo test

Every tree-sitter command, from generate to the tests, runs the CLI of the WillBooster/tree-sitter runtime version locked in Cargo.lock (script/tree-sitter), whose generator and runtime have fixes that the upstream CLI lacks. script/fork-cli downloads that CLI into .tmp/ from its GitHub Release on first use, or builds it with cargo when the download fails or the release has no binary that runs here.

bun run generate records a fresh generation profile from the applicable test/corpus cases and Git-tracked files in examples/, then generates compact parser tables. The parser also embeds metadata from tree-sitter.json. After changing a grammar, tree-sitter.json, a corpus case, or a tracked example, regenerate and commit the affected grammar's src/ directory. Stage added or removed examples with git add -A examples before generation so the profile uses the intended file list. Profiles in .tmp/generation-profiles/ are temporary and must not be committed. bun run build-wasm, bun run build/ci, and the release build regenerate the parsers before compiling them.

bun run test runs:

• the corpus in test/corpus, with the native build and with the Wasm build (the first run downloads the WASI SDK);
• a check that the real-world JavaScript files in examples/, the checked-in ones and those of the cloned repository, fail to parse exactly as listed in script/known-failures.txt. The first run clones the repository. The example repository is pinned to a commit in script/parse-examples. After a grammar change or a moved pin alters that list, script/parse-examples rewrites it; review its diff before committing;
• a performance check (test/unit/performance.test.ts) that recovering from an error on each line takes linear time (ten times the lines take about ten times the CPU time), since consumers parse files while they are being edited. It loads the Wasm build through @willbooster/web-tree-sitter, which bun run build/ci rebuilds after regenerating the parser;
• checks that the Wasm build parses in Chromium (test/unit/browser/) and in Cloudflare Workers with and without Node.js compatibility (test/unit/workers.test.ts). Run bun run test/ci-setup once before the first run to install Chromium and, on Linux, the system libraries it needs;
• a check that package.json and Cargo.lock lock the same WillBooster/tree-sitter runtime version (test/unit/runtimeVersion.test.ts).

The tests and script/parse-examples compile the parser into .tmp/tree-sitter-lib instead of the CLI's cache shared by every checkout, and mise.toml sets TREE_SITTER_LIBDIR to it for any other command run in the checkout.

CI also runs these tests on Linux arm64 and macOS, where the Rust binding compiles the parser natively, and fuzzes the parser with libFuzzer and sanitizers (.github/workflows/robustness.yml).

References

• The ESTree Spec
• The ECMAScript 2025 Spec