promise 手写

promise333.js

@@ -0,0 +1,181 @@
+function resolvePromise(promise2,x,resolve,reject){
+  //判断x是不是promise
+  //规范中规定：我们允许别人乱写，这个代码可以实现我们的promise和别人的promise 进行交互
+  if(promise2 === x){//不能自己等待自己完成
+      return reject(new TypeError('循环引用'));
+  };
+  // x是除了null以外的对象或者函数
+  if(x !=null && (typeof x === 'object' || typeof x === 'function')){
+      let called;//防止成功后调用失败
+      try{//防止取then是出现异常  object.defineProperty
+          let then = x.then;//取x的then方法 {then:{}}
+          if(typeof then === 'function'){//如果then是函数就认为他是promise
+              //call第一个参数是this，后面的是成功的回调和失败的回调
+              then.call(x,y => {//如果Y是promise就继续递归promise
+                  if(called) return;
+                  called = true;
+                  resolvePromise(promise2,y,resolve,reject)
+              },r => { //只要失败了就失败了
+                  if(called) return;
+                  called = true;
+                  reject(r);  
+              });
+          }else{//then是一个普通对象，就直接成功即可
+              resolve(x);
+          }
+      }catch (e){
+          if(called) return;
+          called = true;
+          reject(e)
+      }
+  }else{//x = 123 x就是一个普通值 作为下个then成功的参数
+      resolve(x)
+  }
+
+}
+
+class Promise {
+  constructor (executor){
+      //默认状态是等待状态
+      this.status = 'panding';
+      this.value = undefined;
+      this.reason = undefined;
+      //存放成功的回调
+      this.onResolvedCallbacks = [];
+      //存放失败的回调
+      this.onRejectedCallbacks = [];
+      let resolve = (data) => {//this指的是实例
+          if(this.status === 'pending'){
+              this.value = data;
+              this.status = "resolved";
+              this.onResolvedCallbacks.forEach(fn => fn());
+          }
+
+      }
+      let reject = (reason) => {
+          if(this.status === 'pending'){
+              this.reason = reason;
+              this.status = 'rejected';
+              this.onRejectedCallbacks.forEach(fn => fn());
+          }
+      }
+      try{//执行时可能会发生异常
+          executor(resolve,reject);
+      }catch (e){
+          reject(e);//promise失败了
+      }
+
+  }
+  then(onFuiFilled,onRejected){ 
+      //防止值得穿透 
+      onFuiFilled = typeof onFuiFilled === 'function' ? onFuiFilled : y => y;
+      onRejected = typeof onRejected === 'function' ? onRejected :err => {throw err;}        
+      let promise2;//作为下一次then方法的promise
+     if(this.status === 'resolved'){
+         promise2 = new Promise((resolve,reject) => {
+             setTimeout(() => {
+                try{
+                      //成功的逻辑 失败的逻辑
+                      let x = onFuiFilled(this.value);
+                      //看x是不是promise 如果是promise取他的结果 作为promise2成功的的结果
+                      //如果返回一个普通值，作为promise2成功的结果
+                      //resolvePromise可以解析x和promise2之间的关系
+                      //在resolvePromise中传入四个参数，第一个是返回的promise，第二个是返回的结果，第三个和第四个分别是resolve()和reject()的方法。
+                      resolvePromise(promise2,x,resolve,reject)
+                }catch(e){
+                      reject(e);
+                } 
+             },0)
+         }); 
+     } 
+     if(this.status === 'rejected'){
+          promise2 = new Promise((resolve,reject) => {
+              setTimeout(() => {
+                  try{
+                      let x = onRejected(this.reason);
+                      //在resolvePromise中传入四个参数，第一个是返回的promise，第二个是返回的结果，第三个和第四个分别是resolve()和reject()的方法。
+                      resolvePromise(promise2,x,resolve,reject)
+                  }catch(e){
+                      reject(e);
+                  }
+              },0)
+
+          });
+     }
+     //当前既没有完成也没有失败
+     if(this.status === 'pending'){
+         promise2 = new Promise((resolve,reject) => {
+             //把成功的函数一个个存放到成功回调函数数组中
+              this.onResolvedCallbacks.push( () =>{
+                  setTimeout(() => {
+                      try{
+                          let x = onFuiFilled(this.value);
+                          resolvePromise(promise2,x,resolve,reject);
+                      }catch(e){
+                          reject(e);
+                      }
+                  },0)
+              });
+              //把失败的函数一个个存放到失败回调函数数组中
+              this.onRejectedCallbacks.push( ()=>{
+                  setTimeout(() => {
+                      try{
+                          let x = onRejected(this.reason);
+                          resolvePromise(promise2,x,resolve,reject)
+                      }catch(e){
+                          reject(e)
+                      }
+                  },0)
+              })
+         })
+     }
+     return promise2;//调用then后返回一个新的promise
+  }
+  catch (onRejected) {
+      // catch 方法就是then方法没有成功的简写
+      return this.then(null, onRejected);
+  }
+}
+Promise.all = function (promises) {
+  //promises是一个promise的数组
+  return new Promise(function (resolve, reject) {
+      let arr = []; //arr是最终返回值的结果
+      let i = 0; // 表示成功了多少次
+      function processData(index, data) {
+          arr[index] = data;
+          if (++i === promises.length) {
+              resolve(arr);
+          }
+      }
+      for (let i = 0; i < promises.length; i++) {
+          promises[i].then(function (data) {
+              processData(i, data)
+          }, reject)
+      }
+  })
+}
+// 只要有一个promise成功了 就算成功。如果第一个失败了就失败了
+Promise.race = function (promises) {
+  return new Promise((resolve, reject) => {
+      for (var i = 0; i < promises.length; i++) {
+          promises[i].then(resolve,reject)
+      }
+  })
+}
+// 生成一个成功的promise
+Promise.resolve = function(value){
+  return new Promise((resolve,reject) => resolve(value);
+}
+// 生成一个失败的promise
+Promise.reject = function(reason){
+  return new Promise((resolve,reject) => reject(reason));
+}
+Promise.defer = Promise.deferred = function () {
+  let dfd = {};
+  dfd.promise = new Promise( (resolve, reject) =>  {
+      dfd.resolve = resolve;
+      dfd.reject = reject;
+  });
+  return dfd
+}
+module.exports = Promise;

set与map/js继承.js

@@ -0,0 +1,24 @@
+function F() { }
+var f = new F()
+
+console.log(F.prototype.constructor === F) // true
+console.log(F.__proto__ === Function.prototype) // true
+console.log(Function.prototype.__proto__ === Object.prototype) // true
+console.log(Object.prototype.__proto__ === null) // true
+console.log(Object.__proto__ === Function.prototype) // true
+console.log(Function.__proto__ === Function.prototype) // true
+
+
+console.log(f.__proto__ === F.prototype) // true
+console.log(F.prototype.__proto__ === Object.prototype) // true
+
+
+
+
+if (typeof Object.create !== 'function') {
+  Object.create = (proto) => {
+    function F() { }
+    F.prototype = proto
+    return new F()
+  }
+}

实现一个简单的promise.js

@@ -171,8 +171,8 @@
     Promise.race = function (promises) {
 
     }
-    window.Promise = Promise
-  }(window)
+    global.Promise = Promise
+  }(global)
 
 
 function red() {