提交作业

index.js

@@ -1,41 +1,95 @@
-function myPromise(constructor) {
-  let self = this;
+const PENDING = "pending";
+const FULFILLED = "fulfilled";
+const REJECTED = "rejected";
 
-  self.status = "pending" //定义状态改变前的初始状态
+function MyPromise(constructor) {
+    let self = this;
 
-  self.value = undefined;//定义状态为resolved的时候的状态
+    self.status = PENDING //定义状态改变前的初始状态
+    self.value = undefined;//定义状态为resolved的时候的状态
+    self.reason = undefined;//定义状态为rejected的时候的状态
+    self.fulfilledQueue = [];//fulfilled 回调执行函数队列
+    self.rejectedQueue = [];//rejected 回调执行函数队列
 
-  self.reason = undefined;//定义状态为rejected的时候的状态
+    function resolve(value) {
+        // 状态改变只触发一次（pending-》fulfilled），异步暂时用setTimeout模拟
+        if (self.status === PENDING) {
+            setTimeout(() => {
+                self.status = FULFILLED;
+                self.value = value;
 
-  function resolve(value) {
+                for (let fn of self.fulfilledQueue) {
+                    fn(value);
+                }
+            }, 0);
+        }
+    }
 
-    // TODO resolve如何改变状态及返回结果
+    function reject(reason) {
+        // 状态改变只触发一次（pending-》rejected），异步暂时用setTimeout模拟
+        if (self.status === PENDING) {
+            setTimeout(() => {
+                self.status = REJECTED;
+                self.reason = reason;
 
-  }
+                for (let fn of self.rejectedQueue) {
+                    fn(reason);
+                }
+            }, 0);
+        }
+    }
 
-  function reject(reason) {
+    //捕获构造异常
 
-    // TODO reject如何改变状态及返回结果
+    try {
 
-  }
+        constructor(resolve, reject);
 
-  //捕获构造异常
+    } catch (e) {
 
-  try {
+        reject(e);
 
-    constructor(resolve, reject);
-
-  } catch (e) {
-
-    reject(e);
-
-  }
+    }
 
 }
 
-myPromise.prototype.then = function (onFullfilled, onRejected) {
-
-  //TODO then如何实现
-
+MyPromise.prototype.then = function (onFulfilled, onRejected) {
+    if (this.status === PENDING) {
+        let fulfilledQueue = this.fulfilledQueue;
+        let rejectedQueue = this.rejectedQueue;
+
+        return new MyPromise(function (resolve, reject) {
+            fulfilledQueue.push(function (data) {
+                try {
+                    let value = onFulfilled(data);
+                    resolve(value);
+                } catch (e) {
+                    reject(e);
+                }
+            });
+
+            rejectedQueue.push(function (data) {
+                try {
+                    let value = onRejected(data);
+                    resolve(value);
+                } catch (e) {
+                    reject(e);
+                }
+            })
+        });
+    } else {
+        let value = this.value;
+        let reason = this.reason;
+        let isFulfilled = this.status === FULFILLED;
+        return new MyPromise(function (resolve, reject) {
+            try {
+                let v = isFulfilled ? onFulfilled(value) : onRejected(reason);
+                resolve(v);
+            } catch (e) {
+                reject(e);
+            }
+        });
+    }
 }
-module.exports = myPromise
+
+module.exports = MyPromise