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## Workers
Deno supports
[`Web Worker API`](https://developer.mozilla.org/en-US/docs/Web/API/Worker/Worker).
Workers can be used to run code on multiple threads. Each instance of `Worker`
is run on a separate thread, dedicated only to that worker.
Currently Deno supports only `module` type workers; thus it's essential to pass
`type: "module"` option when creating new worker:
```ts
// Good
new Worker("./worker.js", { type: "module" });
// Bad
new Worker("./worker.js");
new Worker("./worker.js", { type: "classic" });
```
### Using Deno in worker
**UNSTABLE**: This feature is unstable and requires `--unstable` flag
By default `Deno` namespace is not available in worker scope.
To add `Deno` namespace pass `deno: true` option when creating new worker:
```ts
// main.js
const worker = new Worker("./worker.js", { type: "module", deno: true });
worker.postMessage({ filename: "./log.txt" });
// worker.js
self.onmessage = async (e) => {
const { filename } = e.data;
const text = await Deno.readTextFile(filename);
console.log(text);
self.close();
};
// log.txt
hello world
```
```shell
$ deno run --allow-read --unstable main.js
hello world
```
When `Deno` namespace is available in worker scope; the worker inherits parent
process permissions (the ones specified using `--allow-*` flags).
We intend to make permissions configurable for workers.
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