跨域的异步请求三

这部分我们继续增强我们的系统，如强制定的回调函数。参考一些类库，这些回调函数暂定如下几种：

onStart:请求开始时调用。
onSuccess:请求成功时调用，通常后台会返回一个JSON给它做参数。
onTimeout:请求超时时调用，有一个参数，标识其耗时多少毫秒。
onError:请求失败时调用，有一个异常对象做参数。如果超时，我们会自动抛出一个自定义错误。
onComplete:请求完成时调用，为了保证它只执行一次，我们会对它进行包装。

我们需要一些工具函数来完成这个系统，如类型判定，深拷贝，迭代器等。这些我以前在博客也讲过了，不详述了！

var dom = {
       is:function (obj,type) {
         return (type === "Null" && obj === null) ||
           (type === "Undefined" && obj === void 0 ) ||
           Object.prototype.toString.call(obj).slice(8,-1) === type;
       },
       noop:function(){},
       deepcopy:function(result, source){
         for(var key in source) {
           var copy = source[key];
           if(result === copy) continue;//如window.window === window，会陷入死循环，需要处理一下
           if(dom.is(copy,"Object")){
             result[key] = arguments.callee(result[key] || {}, copy);
           }else if(dom.is(copy,"Array")){
             result[key] = arguments.callee(result[key] || [], copy);
           }else{
             result[key] = copy;
           }
         }
         return result;
       },
       each : function(obj,fn,bind){
         for(var i in obj){
           if(obj.hasOwnProperty(i)){
             if(fn.call(bind || obj[i],obj[i],i,obj)===false){
               break
             }
           }
         }
       },
       toQueryString : function (obj) {//将对象转换为查询字符串
         var enc = encodeURIComponent,
         pairs = [],
         regexp = /%20/g,
         backstop = {};
         dom.each(obj,function(value,name){
           if(value != backstop[name]){
             var assign = enc(name).replace(regexp,'+') + "=";
             if(dom.is(value,"Array")){
               dom.each(value,function(el){
                 pairs.push(assign + enc(el).replace(regexp,'+'));
               });
             }else{
               pairs.push(assign + enc(value).replace(regexp,'+'));
             }
           }
         });
         return pairs.join("&"); // String
       },
    
   head:document.getElementsByTagName("head")[0],
       //obj的成员有url,callbackName,callback,data,cache
       jsonp:function(){}
}

然后是系统的主体部分了：

        dom.jsonp = function(obj){
          var self = arguments.callee;
          //=============列队处理======================
          if (self.callbacks.length) {
            setTimeout(function() {self(obj)}, 0);
            return;
          }
          //=============配置对象处理===================
          obj = dom.deepcopy(dom.deepcopy({}, dom.jsonp.settings), obj);
   
         
          var query = dom.toQueryString(obj.data),
          url = obj.url+"?"+ query+"&"+obj.callbackName+"=dom.jsonp.callback",
          script = document.createElement("script"),
          timed_out = false, timeoutID = null,
          destroyScript = function(){
            script.parentNode && script.parentNode.removeChild( script );
          }, old = obj.onComplete;
          obj.startTime = new Date-0;
 
          obj.onComplete = function(){//修正onComplete回调%>
            if(!arguments.callee.done){
              old.call(this,[].slice.call(arguments))
              arguments.callee.done = true;
            }
          }
          //========构建新JS文件上的回调函数==================
          dom.jsonp.addCallback((function(obj){
            return function(){//参数未定，第一个参数肯定为JSON
 
              var args = [].slice.call(arguments)
              try{
                if (!timed_out){//清除timeout引用
                  clearTimeout(timeoutID);
                }else{
                  throw new Error(504,"Gateway Timeout")
                }
                obj.onSuccess.apply(obj,args);
              }catch(e){
                obj.onError.call(null,e);
              }finally{
                obj.onComplete.apply(obj,args);
                destroyScript();
              }
            }
          })(obj));
       //================设置script标签=============
       if(!obj.cache)
            url+= '×tamp='+(new Date-0)
          script.src = url;
          dom.head.appendChild(script);
 
          obj.onStart.call(obj,null);
           
          //===========设置请求超时的相关回调============
          if (obj.timeout){
            timeoutID = setTimeout(function(){
              //如果超时则执行如下回调函数
              timed_out = true;
              var time = new Date  - obj.startTime;
              obj.onTimeout.call(obj,time);
              obj.onComplete.call(obj,null);
              destroyScript();
            },obj.timeout)
          }
 
 
        };
//静态成员
      dom.deepcopy(dom.jsonp, {
        settings : {
          url:location.href,
          callbackName: 'callback',
          cache:false,
          onStart:dom.noop,
          onSuccess:dom.noop,
          onComplete:dom.noop,
          onTimeout:dom.noop,
          onError:dom.noop
        },
        callbacks : [],
        callback :function(){//统一处理回调函数
          var objs = this.callbacks,
          args = [].slice.call(arguments)
          for (var i=0,el;el=objs[i++];) {
            el.apply(null,args)
          }
          this.callbacks = [];
        },
        addCallback : function(obj){
          this.callbacks.push(obj)
        }
      });

<!doctype html>
<html>
  <head>
    <title>jsonp跨域请求 by 司徒正美</title>
    <meta charset="utf-8"/>
    <meta content="IE=8" http-equiv="X-UA-Compatible"/>
    <meta name="keywords" content="jsonp跨域请求 by 司徒正美" />
    <meta name="description" content="jsonp跨域请求 by 司徒正美" />
    <script type="text/javascript" charset="utf-8">

//暴露类库唯一一个全局变量作为命名空间

obj.onComplete = function(){//修正onComplete回调%>
            if(!arguments.callee.done){
              old.call(this,[].slice.call(arguments))
              arguments.callee.done = true;
            }
          }
          //========构建新JS文件上的回调函数==================
          dom.jsonp.addCallback((function(obj){
            return function(){//参数未定，第一个参数肯定为JSON

dom.head.appendChild(script);

obj.onStart.call(obj,null);
          
          //===========设置请求超时的相关回调============
          if (obj.timeout){
            timeoutID = setTimeout(function(){
              //如果超时则执行如下回调函数
              timed_out = true;
              var time = new Date  - obj.startTime;
              obj.onTimeout.call(obj,time);
              obj.onComplete.call(obj,null);
              destroyScript();
            },obj.timeout)
          }

}
      };
      dom.deepcopy(dom.jsonp, {
        settings : {
          url:location.href,
          callbackName: 'callback',
          cache:false,
          onStart:dom.noop,
          onSuccess:dom.noop,
          onComplete:dom.noop,
          onTimeout:dom.noop,
          onError:dom.noop
        },
        callbacks : [],
        callback :function(){//统一处理回调函数
          var objs = this.callbacks,
          args = [].slice.call(arguments)
          for (var i=0,el;el=objs[i++];) {
            el.apply(null,args)
          }
          this.callbacks = [];
        },
        addCallback : function(obj){
          this.callbacks.push(obj)
        }
      });
      window.onload = function(){
        dom.jsonp({
          url:"http://api.flickr.com/services/feeds/photos_public.gne",
          onSuccess:function(json){//现在是测试，理应赋一个空函数
            throw "强制发生错误"
          },
          onStart:function(){
            alert("第一个请求开始了")
          },
          onComplete:function(){
            alert("第一个请求完成了")
          },
          onError:function(e){
            alert("发生[ "+e+" ]错误")
          },

data:{
            tags: 'cat',
            tagmode: 'any',
            format: 'json' },
          callbackName:"jsoncallback"});

dom.jsonp({
          url:"http://api.cnet.com/restApi/v1.0/techProductSearch",
          onSuccess:function(json){
            if(window.JSON){
              alert(window.JSON.stringify(json))
            }
          },
          onStart:function(){
            alert("第二个请求开始了")
          },
          onComplete:function(){
            alert("第二个请求完成了")
          },
          data:{
            partTag: 'mtvo',
            iod: 'hlPrice',
            viewType: 'json',
            results: '100',
            query: 'ipod'},
          callbackName:"callback"});

dom.jsonp({
          onStart:function(){
            alert("第三个请求开始了")
          },
          onSuccess:function(json){
            if(window.JSON){
              alert(window.JSON.stringify(json))
            }
          },
          onComplete:function(){
            alert("第三个请求完成了")
          },
          timeout:400,
          onTimeout:function(t){
            alert("一共耗时"+t+"毫秒")
          },
          onError:function(e){
            alert("发生[ "+e+" ]错误")
          },
          url:"http://del.icio.us/feeds/json/fans/stomita",
          callbackName:"callback"});
        dom.jsonp({
          onStart:function(){
            alert("第四个请求开始了")
          },
          onSuccess:function(json){
            if(window.JSON){
              alert(window.JSON.stringify(json))
            }
          },
          onComplete:function(){
            alert("第四个请求完成了")
          },
          url:"http://api.search.yahoo.com/WebSearchService/V1/webSearch",
          data:{
            appid:"YANCPYV74SDXOZ61",
            output:"json",
            query:"yahoo"
          }
        });

}

</script>

</head>
  <body>
    <h1>JSONP跨域请求by 司徒正美</h1>

</body>
</html>

例子中我们做了各种测试，都能过了，不过除IE外，其他浏览器的执行顺序都朋点絮乱了。这缘于标准浏览器并没有对setTimeout的待执行函数弄成一个队列，看来我们要自行搞一个延迟队列才行了……

var JSONP = function JSONP(url, options) {
	this.options = {callbackParamName: 'callback'};
	for (var prop in options) this.options[prop] = options[prop];
	this.options= options;
	this.url = url;
	this.head = document.getElementsByTagName('head')[0];

	var _this = this;
	this.request();
	if (options.timeout) this.timer = setTimeout(function() {_this.timeoutHandler();}, options.timeout);
}

JSONP.sequence = 0;
JSONP.prototype = {
	constructor: JSONP,

	request: function() {
		var url;
		var script = this.script = document.createElement('script');
		var options = this.options;
		var _this = this;
		this.currentCallbackName = "callback_" + JSONP.sequence++;

		var parameters = this.options.callbackParamName + '=JSONP.' + this.currentCallbackName + '&' + this.composeParams();

		if (this.url.indexOf('?') > -1) url = this.url + '&' + parameters;
		else url = this.url + '?' + parameters;

		JSONP[this.currentCallbackName] = function(json) {
			clearTimeout(_this.timer);
			_this.head.removeChild(script);
			delete JSONP[_this.currentCallbackName];
			if (options.onSuccess) options.onSuccess.call(_this, json);
		};
		script.setAttribute('src', url);
		script.setAttribute('type', 'text/javascript');
		this.head.appendChild(script);
	},

	timeoutHandler: function() {
		if (JSONP[this.currentCallbackName]) {
			JSONP[this.currentCallbackName] = this.nop;
			this.head.removeChild(this.script);
		}
		this.options.onFailure();
	},

	nop: function() {
	},

	composeParams: function() {
		var ret = '';
		var params = this.options.params;
		var tmpArray = [];
		for (var key in params) {
			tmpArray.push(encodeURIComponent(key) + "=" + encodeURIComponent(params[key]));
		}
		return tmpArray.join('&');
	}
}