Structs
The TC39 structs proposal for JavaScript today: structs, shared structs, SharedArray, Atomics.Mutex and Atomics.Condition, with a compiler for their syntax.
This is an implementation of the TC39
structs proposal (Stage 2, the December
2024 draft) for JavaScript today: structs, shared structs, Shared Arrays,
Atomics.Mutex and Atomics.Condition. It has a runtime that follows the
spec's algorithms, and a compiler for the proposal's syntax. In TypeScript, the
compiler also uses the types to make shared struct field access direct.
shared struct Counter {
count = 0;
lock = new Atomics.Mutex();
}
const counter = new Counter();
worker.postMessage(counter); // the same object in the worker, not a copy
// in any agent:
{
using _ = Atomics.Mutex.lock(counter.lock);
counter.count++;
}You can write programs and run them in your browser, with the compiled JavaScript side by side, in the playground.
This grew out of arv/threads, as something much smaller that stays as close to the spec as JavaScript allows. See Differences from the Spec.
What's in It
| Spec | Here |
|---|---|
§1 struct declarations |
The compiler lowers them to classes that call the runtime |
§2 shared struct declarations |
Proxies over one SharedArrayBuffer, the heap |
§2.3 Atomics on struct fields |
load, store, exchange and compareExchange take a struct |
§2.4 Reflect.canBeShared |
Installed on Reflect |
§3 SharedArray |
A global: a Shared Struct with indexed fields and a fixed length |
§4 Atomics.Mutex, UnlockToken |
Futex-style locks on heap words; tokens work with using |
§4 Atomics.Condition |
wait, waitFor (with a timeout and a predicate), notify |
Importing @arv/structs installs the globals. The compiler's output imports
@arv/structs/runtime, which does it too.
Where to Next
- Installing and Running: the packages, the Node hook, the CLI and the compiler's API.
- Structs and Shared Structs: what the syntax makes, and how.
- The Playground: try it all in your browser.