vercel-labs/scriptc v0.4.0

on GitHub

0.4.0

Breaking changes

• tsc-ts is the default TypeScript 7 checker on Linux and macOS. scriptc installs it with the compiler (tsc-ts 0.0.5 and its platform package for the host). Programs get the same diagnostics and generated code as with tsgo, and compiling takes less checker memory. SCRIPTC_CHECKER=tsgo selects tsgo, which stays the default on Windows. A build cache entry made with one checker isn't reused with the other.
• --npm-static=auto, the default, compiles more packages: packages typed by their DefinitelyTyped twin (@types/<name>), and untyped dependencies that another package's JavaScript imports. A program whose dependencies were refused before can now compile them, and a twin whose declarations disagree with the package's JavaScript fails the build at the use. Use --npm-static <pkg,…> to name the packages to compile.
• Program type errors are reported as type errors instead of as refusals of the npm package that contains them.

Highlights

• WebAssembly: builds translate every WebAssembly module whose bytes they can see into native code, and WebAssembly.compile, instantiate, validate, new WebAssembly.Module and new WebAssembly.Instance run them. There is no interpreter. WebAssembly.Memory, Table and Global, Module.imports, Module.exports and Module.customSections, and function references from tables are supported, and modules can be sent to workers. scriptc coverage lists the modules a program loads, with --wasm <file.wasm> for modules loaded from paths the sources don't spell out.
• Async functions that suspend only at their awaits run as stackless coroutines instead of on fibers with their own stack, so a suspended call keeps only the values live across its awaits.
• Discriminated unions of records are the record pointer itself, with no box around each value.
• The dynamic tier computes with NaN-boxed values: numbers, booleans, undefined and null between operators no longer allocate. scriptc coverage --explain-dynamic lists the functions that run in the dynamic tier and why, and --tier=static-only keeps a program fully static.
• npm packages: esbuild's bundled CommonJS chunks, CommonJS cycles and lazily initialized ES modules compile statically, as do classic CommonJS packages (late and JSON requires, require cycles), class hierarchies across a package's modules, and the packages unblocked by type-only imports, @types packages, punycode and constants. chalk 5 and the jose root entry compile.

Features

• @scriptc/experimental adds ThreadSlots, one value per key and thread on shared objects, read without a lock.
• node:test adds mock.timers, getTestContext, t.assert.snapshot and t.assert.fileSnapshot, the TestContext values filePath, attempt, passed, workerId and tags, module-level before and after hooks, the SuiteContext and hook contexts, and unnamed test and describe calls. A timed-out test cancels its running subtests.
• node:worker_threads adds BroadcastChannel, setEnvironmentData/getEnvironmentData, receiveMessageOnPort, markAsUntransferable, markAsUncloneable, threadName, resourceLimits.stackSizeMb, the stdout/stderr/stdin options and streams, and worker[Symbol.asyncDispose].
• node:net adds SocketAddress and BlockList, and net.connect resolves host names.
• node:http pools keep-alive sockets in Agents, uses globalAgent for default requests, reads http.request options at run time, and speaks HTTP over Unix domain sockets. fetch tunnels through HTTP_PROXY/HTTPS_PROXY with CONNECT.
• DisposableStack, Float16Array, Error.isError, Promise.try and the regular expression v flag are supported.
• Iterator helpers run on generators, Map and Set iterators, string and typed array iterators, Iterator.from and untyped iterators.
• Object.groupBy and Map.groupBy group Sets, Maps and generators.
• v8, stream/web, dns/promises, EvalError and graceful-fs are available, and Temporal is reported as absent, as in Node 24.
• util.promisify works over the crypto callback functions, dns lookups, child_process.exec's callback forms and callback-style functions.
• events.once takes an AbortSignal and works over streams.
• AsyncLocalStorage stores carry into timer, immediate, process.nextTick and microtask callbacks.
• JavaScript classes compile like TypeScript classes when their layout or JSDoc types allow it.
• Classes that extend EventEmitter or a stream class can be used as values, and so can EventEmitter, the stream classes and the error classes themselves. Constructor functions can inherit from them.
• Class instances can be frozen and their fields redefined.
• Method overrides may differ from the method they override in parameter and result types, as long as each value converts.
• Library profiles add the cstring class.
• An experimental young-object nursery for compiled classes and records is available at compile time with SCRIPTC_YOUNG_NURSERY=1.

Performance

• Dense arrays have head room, so shift, splice(0, n) and unshift runs cost amortized O(1), and pop of a packed array is inline.
• Index loops over arrays and typed arrays are versioned on one bounds guard, with stable lengths proven and typed-array memory tagged for alias analysis.
• Retain and release pairs are removed through private-array precision and last-use moves, borrowed string slices go into stack buffers, and records, tuples and spread updates stay in frame storage.
• SHA-384 and SHA-512 use AVX2, AVX-512VL or the arm64 SHA-512 instructions, and MD5's block function is unrolled.
• String character tests, optional-string switches, String.fromCharCode and long-string length are faster, and Buffer.write widens ASCII to UTF-16 sixteen bytes per step.
• The cycle collector walks dead cycles once, frees large dead cycle sets in address order and no longer creates self-capture cycles on the release fast path.
• Workers return their memory while the event loop waits and when they finish, and default-region memory is committed as it is used.
• Lifetime regions carry across await, and freed region chunks are reused.
• Large closure environments compile in linear time, and two frontend scans no longer repeat.
• Programs keep stack frames only when they can read stack. Before, a computed-key read on a dynamic value kept frames in every function; tsc-ts's own check is back to 0.3.6's speed.
• The child-process runtime unit links only into programs that spawn.

Fixes

• Node 24 parity: util.format, util.types and util.inspect, URLSearchParams, querystring (null-prototype results), string_decoder, os, events and timers/promises match Node 24. Class instances, iterators, iterator helper objects and holes in arrays print as Node prints them, and %d/%i format dynamic arguments as Node does.
• Silent wrong output is fixed for object identity, Object.prototype values, Date.parse (V8's date grammar), stored builtins, constructor returns, arr && arr[0], ES5 class names, builtin function values, uninitialized let writes, module-export this and 1 ** Infinity.
• Strings compare in UTF-16 code-unit order.
• Dates format with Node's local time zone names, convert to local time once for their local getters, and follow TZ changes. Date.prototype.toJSON gives null for invalid dates.
• Errors: thrown Maps, Sets, typed arrays, functions and arrays keep their identity. Errors list their own name where they were created, errors held as any have their own stack accessor and convert with Error.prototype.toString, and errors that cross into dynamic code carry Node's error properties.
• matchAll rows and exec results have index, input and groups, and named groups keep their null prototype through optional chains.
• Unhandled rejections are reported after each timer and immediate callback, and async generator completions settle on Node's microtask turns.
• Missing Record and index-signature keys read as undefined, and generic functions that read a missing element return undefined.
• Sockets: 'data' listeners get strings after setEncoding, socket and stream chunks are Buffers, and an idle pooled http socket that receives data is destroyed.
• Diagnostic code frames window long source lines.
• npm crashes, internal errors and false TDZ errors found while compiling popular packages are fixed.