Promise机制的深入研究

上一篇文章只是简单的对promise原理有个简单的实现，这次增加了

• all方法,同时调用多次异步请求
• 对resolve和reject方法进行了重构，增加了对多个异步调用的处理
• 对promse进行了改造,除掉了事件触发机制,增加了异步队列

/**
 * Created with JetBrains WebStorm.
 * User: xuwenmin
 * Date: 14-4-26
 * Time: 下午1:01
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 */

var EventEmitter = require('events').EventEmitter;
var http = require('http');
var util = require('util');
// 定义promise对象
var Promise = function(){
    this.queue = [];
    this.isPromise = true;
}
// then 方法为promise/A 规范中的方法
Promise.prototype.then = function(successHandler, errorHandler, progressHandler){
    var hanlder = {};
    if (typeof successHandler == 'function'){
        hanlder.fulfilled =  successHandler;
    }
    if (typeof errorHandler === 'function'){
        hanlder.error =  errorHandler;
    }
    this.queue.push(hanlder);
    return this;
}

// 定义延迟对象
// 包含一个状态和一个promise对象
var Deferred = function(){
    this.promise = new Promise();
}
// 同时处理多个异步的情况
Deferred.prototype.all = function(promises){
    var count = promises.length;
    var that = this;
    var results = [];
    promises.forEach(function(promise, i){
        promise.then(function(data){
            count--;
            results[i] = data;
            // 如果执行玩了，则调用完成方法
            if(count == 0){
                that.resolve(results);
            }
        }, function(err){
            that.reject(err);
        });
    });
    return this.promise;
}
// 生成回调函数
Deferred.prototype.callback = function(){
    var that = this;
    return function(err, data){
        if(err){
            that.reject(err);
        }else{
            that.resolve(data);
        }
    };
}
Deferred.prototype.resolve = function(obj){
      var promise = this.promise;
      var handler;
      while((handler = promise.queue.shift())){
          if (handler && handler.fulfilled){
              var ret = handler.fulfilled(obj);
              if(ret && ret.isPromise){
                  ret.queue = promise.queue;
                  this.promise = ret;
                  return;
              }
          }
      }
}
Deferred.prototype.reject = function(err){
       var promise = this.promise;
       var handler;
       while((handler = promise.queue.shift())){
           if (handler && handler.error){
               var ret = handler.error(err);
               if(ret && ret.isPromise){
                   ret.queue = promise.queue;
                   this.promise = ret;
                   return;
               }
           }
       }
}

var client1 = function(){
    var options = {
        hostname:'www.baidu.com',
        port:80,
        path:'/',
        method: 'get'
    };
    var deferred = new Deferred();
    var req = http.request(options, function(res){
        res.setEncoding('utf-8');
        var data = '';
        res.on('data', function(chunk){
            data += chunk;
        });
        res.on('end', function(){
            deferred.resolve(data);
        });

    });
    req.on('error', function(err){
        deferred.reject(err);
    })
    req.end();
    return deferred.promise;
}
var client2 = function(predata){
    var options = {
        hostname:'www.hao123.com',
        port:80,
        path:'/',
        method: 'get'
    };
    var deferred = new Deferred();
    var req = http.request(options, function(res){
        res.setEncoding('utf-8');
        var data = '';
        res.on('data', function(chunk){
            data += chunk;
        });
        res.on('end', function(){
            data += predata;
            deferred.resolve(data);
        });
    });
    req.on('error', function(err){
        deferred.reject(err);
    })
    req.end();
    return deferred.promise;
}
//
client1().then(function(msg){
    return client2(msg);
}).then(function(data){
    console.log('\033[96m 两次请求的总数据:\033[39m',data);
});

总结

上面的代码参考了深入浅出NodeJS,权当心得体会.