add async

JS/Async/generator.js

@@ -3,7 +3,7 @@ const bluebird = require('bluebird');
 const readFile = bluebird.promisify(fs.readFile);
 
 /**
- * 对应 promise 中的解决回调地狱部分
+ * 读取A--->读取B--->读取C
  */
 function* read() {
     let info = yield readFile('./JS/Async/data/info.txt', 'utf-8');

JS/Async/my_async.js

@@ -0,0 +1,101 @@
+const fs = require('fs');
+const bluebird = require('bluebird');
+const readFile = bluebird.promisify(fs.readFile);
+const co = require('co');
+/**
+ * 假设要实现以下功能:
+ * 先读取A--->再读取B--->最后读取C
+ */
+function* read() {
+    let info = yield readFile('./JS/Async/data/info.txt', 'utf-8');
+    let base = yield readFile(info, 'utf-8');
+    let age = yield readFile(base, 'utf-8');
+    return age;
+}
+
+/**
+ * 不考虑封装的情况，我们可以写出下面的代码
+ */
+// let it = read();
+// let { value, done } = it.next();
+// value.then((data) => {
+//     let { value, done } = it.next(data); //data赋值给了 info
+//     value.then((data) => {
+//         let { value, done } = it.next(data); //data赋值给了 base
+//         value.then((data) => {
+//             let { value, done } = it.next(data); //data赋值给base
+//             //此时done为false
+//             return value;
+//         });
+//     });
+// });
+
+/**
+ * 可以看出上面的代码，其实是重复的，我们可以进行封装
+ */
+
+function my_co(it) {
+    return new Promise((resolve, reject) => {
+        function next(data) {
+            try {
+                var { value, done } = it.next(data);
+
+            }catch(e){
+                return reject(e);
+            }
+            if (!done) { 
+                //done为true,表示迭代完成
+                //value 不一定是 Promise，可能是一个普通值。使用 Promise.resolve 进行包装。
+                Promise.resolve(value).then(val => {
+                    next(val);
+                }, reject);
+            } else {
+                resolve(value);
+            }
+        }
+        next(); //执行一次next
+    });
+}
+function* test() {
+    yield new Promise((resolve, reject) => {
+        setTimeout(resolve, 100);
+    });
+    yield new Promise((resolve, reject) => {
+        // throw Error(1);
+        resolve(10)
+    });
+    yield 10;
+    return 1000;
+}
+
+my_co(test()).then(data => {
+    console.log(data); //输出22
+}).catch((err) => {
+    console.log('err: ', err);
+});
+
+
+my_co(read()).then(data => {
+    console.log(data);
+}).catch((err) => {
+    console.log('err: ', err);
+});
+
+
+/**
+ * async 是 await 的语法糖。
+ * 以上需要使用 async/await 实现
+ */
+
+async function readAsync() {
+    let info = await readFile('./JS/Async/data/info.txt', 'utf-8');
+    let base = await readFile(info, 'utf-8');
+    let age = await readFile(base, 'utf-8');
+    return age;
+}
+
+readAsync().then((data) => {
+    console.log('async: ' + data);
+}).catch(err => {
+    console.log(err);
+});