Week 2 , homework8

index.js

@@ -7,16 +7,28 @@ function myPromise(constructor) {
 
   self.reason = undefined;//定义状态为rejected的时候的状态
 
+  self.onResolvedCallbacks = []; // 成功调用函数数组
+  self.onRejectedCallbacks = []; // 失败调用函数数组
+
   function resolve(value) {
 
     // TODO resolve如何改变状态及返回结果
+    if (self.status === 'pending') {
+      self.status = 'fulfilled';
+      self.value = value;
+      self.onResolvedCallbacks.forEach(fn => fn());
+    }
 
   }
 
   function reject(reason) {
 
     // TODO reject如何改变状态及返回结果
-
+    if (self.status === 'pending') {
+      self.status = 'rejected';
+      self.reason = reason;
+      self.onRejectedCallbacks.forEach(fn => fn());
+    }
   }
 
   //捕获构造异常
@@ -33,9 +45,101 @@ function myPromise(constructor) {
 
 }
 
-myPromise.prototype.then = function (onFullfilled, onRejected) {
+// A+规范规定，让不同的promise代码互相套用
+function resolvePromise(promise2, x, resolve, reject) {
+  // 循环引用报错
+  if (x === promise2) {
+    return reject(new TypeError('promise循环引用'))
+  }
+  // 防止多次调用
+  let called;
+  // x不是null且x是对象或者函数
+  if (x != null && (typeof x === 'object' || typeof x === 'function')) {
+    try {
+      // A+规范规定，声明then = x的then方法
+      let then = x.then;
+      // 如果then是函数，默认是promise了
+      if (typeof then === 'function') {
+        // 就让then执行 第一个参数是this, 后面是成功的回调和失败的回调
+        then.call(x, y => {
+          if (called) return;
+          called = true;
+          // resolve的结果依旧是promise那就继续解析
+          resolvePromise(promice2, y, resolve, reject);
+        }, err => {
+          if (called) return;
+          called = true;
+          reject(err);
+        })
+      } else {
+        resolve(x);
+      }
+    } catch (e) {
+      if (called) return;
+      called = true;
+      reject(e);
+    }
+  } else {
+    resolve(x);
+  }
+}
 
-  //TODO then如何实现
+myPromise.prototype.then = function (onFullfilled, onRejected) {
 
+  // TODO then如何实现
+  // onFulfilled如果不是函数，就忽略onFulfilled，直接返回value
+  onFullfilled = typeof onFullfilled === 'function' ? onFullfilled : value => value;
+  // onRejected如果不是函数，就忽略onRejected，直接扔出错误
+  onRejected = typeof onRejected === 'function' ? onRejected : err => { throw err };
+  let promise2 = new Promise((resolve, reject) => {
+    if (this.status === 'fulfilled') {
+      // 异步
+      setTimeout(() => {
+        try {
+          let x = onFullfilled(this.value);
+          resolvePromise(promise2, x, resolve, reject);
+        } catch (e) {
+          reject(e);
+        }
+      }, 0);
+    }
+    if (this.status === 'rejected') {
+      // 异步
+      setTimeout(() => {
+        try {
+          let x = onRejected(this.reason);
+          resolvePromise(promise2, x, resolve, reject);
+        } catch(e) {
+          reject(e);
+        }
+      });
+    }
+    if (this.status === 'pending') {
+      this.onResolvedCallbacks.push(() => {
+        // 异步
+        setTimeout(() => {
+          try {
+            let x = onFulfilled(this.value);
+            resolvePromise(promise2, x, resolve, reject);
+          } catch (e) {
+            reject(e);
+          }
+        }, 0);
+      });
+      this.onRejectedCallbacks.push(() => {
+        // 异步
+        setTimeout(() => {
+          try {
+            let x = onRejected(this.reason);
+            resolvePromise(promise2, x, resolve, reject);
+          } catch (e) {
+            reject(e);
+          }
+        }, 0)
+      });
+    };
+  });
+
+  return promise2;
 }
 module.exports = myPromise