<script type="text/javascript"> function Ajax(){ var xhr; if(window.XMLHttpRequest){ xhr=new XMLHttpRequest(); }else{ try{xhr=new ActiveXObject("MSXML2.XMLHTTP.6.0");}catch(e){} try{xhr=new ActiveXObject("MSXML2.XMLHTTP");}catch(e){} } if(!xhr) return; this.Xhr=xhr; //用属性存储XMLHttpRequest对象的实例 } Ajax.prototype.send=function(url,options){ if(!this.Xhr) return; var xhr=this.Xhr; var aborted=false; var _options={ //提供默认值 method:"GET", timeout:5000, onerror:function(){}, onsuccess:function(){} }; for(var o in options){ //覆盖掉原来的默认值 _options[o]=options[o]; } function checkForTimeout(){ //检查是否超时的情况 if(xhr.readyState!=4){ aborted=true; xhr.abort(); //取消本次传输 } } //在规定的时间内检查readyState属性的值 setTimeout(checkForTimeout,_options.timeout); function onreadystateCallback(){ if(xhr.readyState==4){ /* * 注释：状态码在200内表示成功，300内表示重定向，400内是客户端错误，500是服务器端错误 */ if(!aborted && xhr.status>=200 && xhr.status<300){ //检查aborted属性是否超时 _options.onsuccess(xhr); }else{ _options.onerror(xhr); } } } xhr.open(_options.method,url,true); xhr.onreadystatechange=onreadystateCallback; xhr.send(null); } var ajax=new Ajax(); ajax.send("test.php",{method: GET ,timeout:100,onerror:onerror,onsuccess:onsuccess}); function onerror(xhr){ alert("Timeout"); } function onsuccess(xhr){ alert(xhr.responseText); } </script>