pref: remove await/async from internal async calls

src/util/async.ts

@@ -0,0 +1,75 @@
+import { isFunction } from './underscore'
+
+type resolver = (x?: any) => Thenable
+
+interface Thenable {
+  then (resolve: resolver, reject?: resolver): Thenable;
+  catch (reject: resolver): Thenable;
+}
+
+function mkResolve (value: any) {
+  const ret = {
+    then: (resolve: resolver) => resolve(value),
+    catch: () => ret
+  }
+  return ret
+}
+
+function mkReject (err: Error) {
+  const ret = {
+    then: (resolve: resolver, reject?: resolver) => {
+      if (reject) return reject(err)
+      return ret
+    },
+    catch: (reject: resolver) => reject(err)
+  }
+  return ret
+}
+
+function isThenable (val: any): val is Thenable {
+  return val && isFunction(val.then)
+}
+
+function isCustomIterable (val: any): val is IterableIterator<any> {
+  return val && isFunction(val.next) && isFunction(val.throw) && isFunction(val.return)
+}
+
+export function toThenable (val: IterableIterator<any> | Thenable): Thenable {
+  if (isThenable(val)) return val
+  if (isCustomIterable(val)) return reduce()
+  return mkResolve(val)
+
+  function reduce (prev?: any): Thenable {
+    let state
+    try {
+      state = (val as IterableIterator<any>).next(prev)
+    } catch (err) {
+      return mkReject(err)
+    }
+
+    if (state.done) return mkResolve(state.value)
+    return toThenable(state.value!).then(reduce, err => {
+      let state
+      try {
+        state = (val as IterableIterator<any>).throw!(err)
+      } catch (e) {
+        return mkReject(e)
+      }
+      if (state.done) return mkResolve(state.value)
+      return reduce(state.value)
+    })
+  }
+}
+
+export function toValue (val: IterableIterator<any> | Thenable) {
+  let ret: any
+  toThenable(val)
+    .then((x: any) => {
+      ret = x
+      return mkResolve(ret)
+    })
+    .catch((err: Error) => {
+      throw err
+    })
+  return ret
+}