fix fix yield.

helpers.ts

@@ -0,0 +1,9 @@
+export async function yieldThread() {
+  return new Promise(resolve => {
+    const ch = new MessageChannel()
+    // @ts-ignore (typescript thinks this property should be called `addListener`, but in fact it's `addEventListener`)
+    ch.port1.addEventListener('message', resolve)
+    ch.port2.postMessage(0)
+    ch.port1.start()
+  })
+}