feat: async to generator

Author: sl1673495

async-to-generator.js

@@ -0,0 +1,64 @@
+/**
+ * async的执行原理
+ * 其实就是自动执行generator函数
+ * 暂时不考虑genertor的编译步骤（更复杂）
+ */
+
+const getData = () =>
+  new Promise(resolve => setTimeout(() => resolve("data"), 1000))
+
+// 这样的一个async函数 应该再1秒后打印data
+async function test() {
+  const data = await getData()
+  
+  console.log(data)
+  return data
+}
+
+// async函数会被编译成generator函数 (babel会编译成更本质的形态，这里我们直接用generator)
+function* testG() {
+  // await被编译成了yield
+  const data = yield getData()
+  console.log('data: ', data);
+  const data2 = yield getData()
+  console.log('data2: ', data2);
+  return data + '123'
+}
+
+function asyncToGenerator(generatorFunc) {
+  return function() {
+    const gen = generatorFunc.apply(this, arguments)
+
+    return new Promise((resolve, reject) => {
+      function step(key, arg) {
+        let generatorResult
+        try {
+          generatorResult = gen[key](arg)
+        } catch (error) {
+          return reject(error)
+        }
+
+        const { value, done } = generatorResult
+
+        if (done) {
+          return resolve(value)
+        } else {
+          return Promise.resolve(value).then(
+            function onResolve(val) {
+              step("next", val)
+            },
+            function onReject(err) {
+              step("throw", err)
+            },
+          )
+        }
+      }
+      step("next")
+    })
+  }
+}
+
+const testGAsync = asyncToGenerator(testG)
+testGAsync().then(result => {
+  console.log(result)
+})