javascript通过单体模式、闭包封装一次嗅探浏览器api

<script type="text/javascript">

var SimpleXhrFactory=(function(){

var standard={

createXhrObject:function(){

return new XMLHttpRequest();

}

};

var activeXNew={

createXhrObject:function(){

return new ActiveXObject('Msxml2.XMLHTTP');

}

};

var activeXOld={

createXhrObject:function(){

return new ActiveXObject('Microsoft.XMLHTTP');

}

};

var testObject;

try{

testObject=standard.createXhrObject();

return standard;

}catch(e){

try{

testObject=activeXNew.createXhrObject();

return testObject;

}catch(e){

try {

testObject = activeXOld.createXhrObject();

}catch (e){

throw new Error('No XHR object found in this environment.');

}

}

}

})();

var xhr=SimpleXhrFactory.createXhrObject();

alert(xhr.toString());

</script>