Added support for async iterators

CHANGELOG.md

@@ -19,6 +19,7 @@ The changes mentioned here are discussed in detail in the [release highlights](h
 * `toJS` now accepts the options: `{ detectCycles?: boolean, exportMapsAsObjects?: boolean }`, both `true` by default
 * Introduced `flow` to create a chain of async actions. This is the same function as [`asyncActions`](https://github.com/mobxjs/mobx-utils#asyncaction) of the mobx-utils package
 * These `flow`'s are now cancellable, by calling `.cancel()` on the returned promise, which will throw a cancellation exception into the generator function.
+* `flow` also has experimental support for async iterators (`async * function`)
 * The flow typings have been updated. Since this is a manual effort, there can be mistakes, so feel free to PR!
 
 * `computed(fn, options?)` / `@computed(options) get fn()` now accept the following options:

src/api/flow.ts

@@ -154,6 +154,11 @@ export function createFlowGenerator(name: string, generator: Function) {
             }
 
             function next(ret: any) {
+                if (ret && typeof ret.then === "function") {
+                    // an async iterator
+                    ret.then(next, reject)
+                    return
+                }
                 if (ret.done) return resolve(ret.value)
                 pendingPromise = Promise.resolve(ret.value) as any
                 return pendingPromise!.then(onFulfilled, onRejected)

test/base/typescript-tests.ts

@@ -1579,3 +1579,59 @@ test("it should support asyncAction as decorator (babel)", async () => {
 
     expect(await x.f(3)).toBe(16)
 })
+
+test("flow support async generators", async () => {
+    ;(Symbol as any).asyncIterator =
+        (Symbol as any).asyncIterator || Symbol.for("Symbol.asyncIterator")
+
+    async function* someNumbers() {
+        await Promise.resolve()
+        yield 1
+        await Promise.resolve()
+        yield 2
+        await Promise.resolve()
+        yield 3
+    }
+
+    let steps = 0
+    const start = mobx.flow(async function*() {
+        let total = 0
+        for await (const number of someNumbers()) {
+            total += number
+        }
+        return total
+    })
+
+    const p = start()
+    const res = await p
+    expect(res).toBe(6)
+})
+
+test.only("flow support throwing async generators", async () => {
+    ;(Symbol as any).asyncIterator =
+        (Symbol as any).asyncIterator || Symbol.for("Symbol.asyncIterator")
+
+    async function* someNumbers() {
+        await Promise.resolve()
+        yield 1
+        await Promise.resolve()
+        throw "OOPS"
+    }
+
+    let steps = 0
+    const start = mobx.flow(async function*() {
+        let total = 0
+        for await (const number of someNumbers()) {
+            total += number
+        }
+        return total
+    })
+
+    const p = start()
+    try {
+        await p
+        fail()
+    } catch (e) {
+        expect("" + e).toBe("OOPS")
+    }
+})

test/tsconfig.json

@@ -2,9 +2,11 @@
     "compilerOptions": {
         "module": "commonjs",
         "target": "es5",
+        "lib": ["esnext"],
         "noImplicitAny": true,
         "sourceMap": false,
         "experimentalDecorators": true,
-        "strict":true
+        "strict":true,
+        "downlevelIteration": true
     }
 }

tsconfig.json

@@ -13,6 +13,7 @@
         "noUnusedLocals": true,
         "noImplicitAny": false,
         "moduleResolution": "node",
+        "downlevelIteration": true,
         "lib": [
             "es6"
         ]