创建xhr时异常处理-Ajax之六

前面几篇一直采用最精简的方式创建Ajax的核心XMLHttpRequest对象

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1	var xhr = window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject('Microsoft.XMLHTTP');

没有考虑其可能出现的异常，即创建失败。其实个人认为以上创建方式创建失败的几率非常之少，起码在IE6/7/8/Firefox/Safari/Chrome/Opera如此，其它浏览器就不知了。

但作为一个基础库还是完善下，如果出现创建失败，failure的第二个参数msg将会被赋值为"create xhr failed"。

如下

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var xhr = function(){     try{         return new XMLHttpRequest();     }catch(e){         try{             return new ActiveXObject('Msxml2.XMLHTTP');         }catch(e){             try{                 return new ActiveXObject('Microsoft.XMLHTTP');             }catch(e){                 failure(null,'create xhr failed',e);             }         }     } }();

完整源码

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Ajax = function(){     function request(url,opt){         function fn(){}         opt = opt || {};         var async   = opt.async !== false,             method  = opt.method    || 'GET',             type    = opt.type      || 'text',             encode  = opt.encode    || 'UTF-8',             timeout = opt.timeout   || 0,             data    = opt.data      || null,             success = opt.success   || fn,             failure = opt.failure   || fn;             method  = method.toUpperCase();         if(data && typeof data == 'object'){//对象转换成字符串键值对             data = _serialize(data);         }         if(method == 'GET' && data){             url += (url.indexOf('?') == -1 ? '?' : '&') + data;             data = null;         }         var xhr = function(){             try{                 return new XMLHttpRequest();             }catch(e){                 try{                     return new ActiveXObject('Msxml2.XMLHTTP');                 }catch(e){                     try{                         return new ActiveXObject('Microsoft.XMLHTTP');                     }catch(e){                         failure(null,'create xhr failed',e);                     }                 }             }         }();         if(!xhr){return;}         var isTimeout = false, timer;         if(async && timeout>0){             timer = setTimeout(function(){                 xhr.abort();                 isTimeout = true;             },timeout);         }         xhr.onreadystatechange = function(){             if (xhr.readyState == 4 && !isTimeout){                 _onStateChange(xhr, type, success, failure);                 clearTimeout(timer);             }else{}         };         xhr.open(method,url,async);         if(method == 'POST'){             xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded;charset=' + encode);         }         xhr.send(data);         return xhr;     }     function _serialize(obj){         var a = [];         for(var k in obj){             var val = obj[k];             if(val.constructor == Array){                 for(var i=0,len=val.length;i<len;i++){                     a.push(k + '=' + encodeURIComponent(val[i]));                 }                           }else{                 a.push(k + '=' + encodeURIComponent(val));             }                       }         return a.join('&');     }     function _onStateChange(xhr,type,success,failure){         var s = xhr.status, result;         if(s>= 200 && s < 300){             switch(type){                 case 'text':                     result = xhr.responseText;                     break;                 case 'json':                     result = function(str){                         return (new Function('return ' + str))();                     }(xhr.responseText);                     break;                 case 'xml':                     result = xhr.responseXML;                     break;             }             success(result);         }else if(s===0){             failure(xhr,'request timeout');         }else{             failure(xhr,xhr.status);         }         xhr = null;     }     return (function(){         var Ajax = {request:request}, types = ['text','json','xml'];         for(var i=0,len=types.length;i<len;i++){             Ajax[types[i]] = function(i){                 return function(url,opt){                     opt = opt || {};                     opt.type = types[i];                     return request(url,opt);                 }             }(i);         }         return Ajax;     })(); }();

 

相关：

ajax_06.zip

https://github.com/snandy/io