Two workers & worker termination (#198)

* Refactoring codecs

* Plugging in new processor

* Fixing decorator

* MozJPEG free issue

* Better worker aborting, and terminate workers that aren't used for 10 seconds

* Better comment

* Ooops, half-typed comment

* Uncommenting problematic line

* Surma fixed it!

* Abstracting WASM initialisation

* Better comment

* Don't need this.

* Adding ticket

* noInitalRun

* Reverting MozJPEG issue demo

* Making a const for worker timeout

* Inline docs

* Bail early rather than nesting

* Addressing nits

src/codecs/util.ts

@@ -0,0 +1,27 @@
+type ModuleFactory<M extends EmscriptenWasm.Module> = (
+  opts: EmscriptenWasm.ModuleOpts,
+) => M;
+
+export function initWasmModule<T extends EmscriptenWasm.Module>(
+  moduleFactory: ModuleFactory<T>,
+  wasmUrl: string,
+): Promise<T> {
+  return new Promise((resolve) => {
+    const module = moduleFactory({
+      // Just to be safe, don't automatically invoke any wasm functions
+      noInitialRun: true,
+      locateFile(url: string): string {
+        // Redirect the request for the wasm binary to whatever webpack gave us.
+        if (url.endsWith('.wasm')) return wasmUrl;
+        return url;
+      },
+      onRuntimeInitialized() {
+        // An Emscripten is a then-able that resolves with itself, causing an infite loop when you
+        // wrap it in a real promise. Delete the `then` prop solves this for now.
+        // https://github.com/kripken/emscripten/issues/5820
+        delete (module as any).then;
+        resolve(module);
+      },
+    });
+  });
+}